Polymorphism in the peroxisome proliferator-activated receptor alpha gene influences the risk for Alzheimer's disease

Defining a vitamin A5/X specific deficiency - vitamin A5/X as a critical dietary factor for mental health

A healthy and balanced diet is an important factor to assure a good functioning of the central and peripheral nervous system. Retinoid X receptor (RXR)-mediated signaling was identified as an important mechanism of transmitting major diet-dependent physiological and nutritional signaling such as the control of myelination and dopamine signalling. Recently, vitamin A5/X, mainly present in vegetables as provitamin A5/X, was identified as a new concept of a vitamin which functions as the nutritional precursor for enabling RXR-mediated signaling. The active form of vitamin A5/X, 9-cis-13,14-dehydroretinoic acid (9CDHRA), induces RXR-activation, thereby acting as the central switch for enabling various heterodimer-RXR-signaling cascades involving various partner heterodimers like the fatty acid and eicosanoid receptors/peroxisome proliferator-activated receptors (PPARs), the cholesterol receptors/liver X receptors (LXRs), the vitamin D receptor (VDR), and the vitamin A(1) receptors/retinoic acid receptors (RARs). Thus, nutritional supply of vitamin A5/X might be a general nutritional-dependent switch for enabling this large cascade of hormonal signaling pathways and thus appears important to guarantee an overall organism homeostasis. RXR-mediated signaling was shown to be dependent on vitamin A5/X with direct effects for beneficial physiological and neuro-protective functions mediated systemically or directly in the brain. In summary, through control of dopamine signaling, amyloid β-clearance, neuro-protection and neuro-inflammation, the vitamin A5/X - RXR - RAR - vitamin A(1)-signaling might be "one of" or even "the" critical factor(s) necessary for good mental health, healthy brain aging, as well as for preventing drug addiction and prevention of a large array of nervous system diseases. Likewise, vitamin A5/X - RXR - non-RAR-dependent signaling relevant for myelination/re-myelination and phagocytosis/brain cleanup will contribute to such regulations too. In this review we discuss the basic scientific background, logical connections and nutritional/pharmacological expert recommendations for the nervous system especially considering the ageing brain.

PPARα Signaling: A Candidate Target in Psychiatric Disorder Management

Peroxisome proliferator-activator receptors (PPARs) regulate lipid and glucose metabolism, control inflammatory processes, and modulate several brain functions. Three PPAR isoforms have been identified, PPARα, PPARβ/δ, and PPARγ, which are expressed in different tissues and cell types. Hereinafter, we focus on PPARα involvement in the pathophysiology of neuropsychiatric and neurodegenerative disorders, which is underscored by PPARα localization in neuronal circuits involved in emotion modulation and stress response, and its role in neurodevelopment and neuroinflammation. A multiplicity of downstream pathways modulated by PPARα activation, including glutamatergic neurotransmission, upregulation of brain-derived neurotrophic factor, and neurosteroidogenic effects, encompass mechanisms underlying behavioral regulation. Modulation of dopamine neuronal firing in the ventral tegmental area likely contributes to PPARα effects in depression, anhedonia, and autism spectrum disorder (ASD). Based on robust preclinical evidence and the initial results of clinical studies, future clinical trials should assess the efficacy of PPARα agonists in the treatment of mood and neurodevelopmental disorders, such as depression, schizophrenia, and ASD.

Carnitine palmitoyltransferase 1 (CPT1) alleviates oxidative stress and apoptosis of hippocampal neuron in response to beta-Amyloid peptide fragment Aβ25-35

CPT1C, which is expressed in hippocampus, influences ceramide level, endogenous cannabinoid and oxidation process, as well as plays an important role in various brain functions such as learning. This study aimed to investigate the role of CPT1C in Alzheimer's disease (AD) and its underlying mechanism. We established a model of Alzheimer's disease in vitro by exposing primary hippocampal neurons to beta-Amyloid peptide fragment 25-35 (Aβ25-35). The cell viability, lactate dehydrogenase (LDH) level, expressions of reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) were detected using Cell Counting Kit-8 (CCK-8), LDH assay, ROS kits, malondialdehyde (MDA) kits and SOD kits, respectively. Moreover, the expression of oxidative stress-related proteins as well as the expressions of amyloid precursor protein (App), p-Tau andβ-site APP-cleaving enzyme1 (Bace-1) were measured using quantitative reverse transcription PCR (RT-qPCR) and western blot. Tunel and western blot were adopted to detect apoptosis as well as its related proteins. After the treatment of peroxisome proliferators-activated receptor alpha (PPARα), CPT1C expression was detected with the application of RT-qPCR and western blot. CPT1C expression was reduced in Aβ25-35-induced HT22 cells. Overexpression of CPT1C relieved cell viability and toxic injury as well as attenuated oxidative stress, apoptosis and expression levels of AD marker proteins. Moreover, higher doses of PPARα agonist activate the expression of CPT1C in Aβ25-35-induced HT22 cells. In conclusion, CPT1C alleviates Aβ25-35-induced oxidative stress, apoptosis and deposition of AD marker proteins in hippocampal neurons, suggesting that CPT1C has favorable effects on alleviating AD and participates in PPARα activation.

Regulation of PPARα by APP in Alzheimer disease affects the pharmacological modulation of synaptic activity

Among genetic susceptibility loci associated with late-onset Alzheimer disease (LOAD), genetic polymorphisms identified in genes encoding lipid carriers led to the hypothesis that a disruption of lipid metabolism could promote disease progression. We previously reported that amyloid precursor protein (APP) involved in Alzheimer disease (AD) physiopathology impairs lipid synthesis needed for cortical networks' activity and that activation of peroxisome proliferator-activated receptor α (PPARα), a metabolic regulator involved in lipid metabolism, improves synaptic plasticity in an AD mouse model. These observations led us to investigate a possible correlation between PPARα function and full-length APP expression. Here, we report that PPARα expression and activation were inversely related to APP expression both in LOAD brains and in early-onset AD cases with a duplication of the APP gene, but not in control human brains. Moreover, human APP expression decreased PPARA expression and its related target genes in transgenic mice and in cultured cortical cells, while opposite results were observed in APP-silenced cortical networks. In cultured neurons, APP-mediated decrease or increase in synaptic activity was corrected by a PPARα-specific agonist and antagonist, respectively. APP-mediated control of synaptic activity was abolished following PPARα deficiency, indicating a key function of PPARα in this process.

The role of peroxisome proliferator-activated receptors in healthy and diseased eyes

Peroxisome Proliferator-Activated Receptors (PPARs) are a family of nuclear receptors that play essential roles in modulating cell differentiation, inflammation, and metabolism. Three subtypes of PPARs are known: PPAR-alpha (PPARα), PPAR-gamma (PPARγ), and PPAR-beta/delta (PPARβ/δ). PPARα activation reduces lipid levels and regulates energy homeostasis, activation of PPARγ results in regulation of adipogenesis, and PPARβ/δ activation increases fatty acid metabolism and lipolysis. PPARs are linked to various diseases, including but not limited to diabetes, non-alcoholic fatty liver disease, glaucoma and atherosclerosis. In the past decade, numerous studies have assessed the functional properties of PPARs in the eye and key PPAR mechanisms have been discovered, particularly regarding the retina and cornea. PPARγ and PPARα are well established in their functions in ocular homeostasis regarding neuroprotection, neovascularization, and inflammation, whereas PPARβ/δ isoform function remains understudied. Naturally, studies on PPAR agonists and antagonists, associated with ocular pathology, have also gained traction with the development of PPAR synthetic ligands. Studies on PPARs has significantly influenced novel therapeutics for diabetic eye disease, ocular neuropathy, dry eye, and age-related macular degeneration (AMD). In this review, therapeutic potentials and implications will be highlighted, as well as reported adverse effects. Further investigations are necessary before any of the PPARs ligands can be utilized, in the clinics, to treat eye diseases. Future research on the prominent role of PPARs will help unravel the complex mechanisms involved in order to prevent and treat ocular diseases.

Nuclear receptors, the aryl hydrocarbon receptor, and macrophage function

Nuclear receptors (NRs) are key regulators of innate immune responses and tissue homeostasis. Evidence indicates that NRs significantly impact steady-state immune regulation, uptake and processing of apoptotic cells, tolerance induction, and control of inflammatory immunity. In this review, we describe our current understanding of the NR activity for balancing inflammation and tolerance, the signaling cascade inducing the NR activation and functional responses, and different mechanisms of the NR-driven immune effects in the context of autoimmune diseases. We further describe the ligand-activated transcription factor the aryl hydrocarbon receptor (AhR) that exhibits analogous functionality. Moreover, we will discuss the putative role of NRs and AhR in immune regulation and disease pathogenesis providing a rationale for therapeutic targeting as a unique opportunities in the clinical management of autoimmune diseases.

Alzheimer's Disease, a Lipid Story: Involvement of Peroxisome Proliferator-Activated Receptor α

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Mutations in genes encoding proteins involved in amyloid-β peptide (Aβ) production are responsible for inherited AD cases. The amyloid cascade hypothesis was proposed to explain the pathogeny. Despite the fact that Aβ is considered as the main culprit of the pathology, most clinical trials focusing on Aβ failed and suggested that earlier interventions are needed to influence the course of AD. Therefore, identifying risk factors that predispose to AD is crucial. Among them, the epsilon 4 allele of the apolipoprotein E gene that encodes the major brain lipid carrier and metabolic disorders such as obesity and type 2 diabetes were identified as AD risk factors, suggesting that abnormal lipid metabolism could influence the progression of the disease. Among lipids, fatty acids (FAs) play a fundamental role in proper brain function, including memory. Peroxisome proliferator-activated receptor α (PPARα) is a master metabolic regulator that regulates the catabolism of FA. Several studies report an essential role of PPARα in neuronal function governing synaptic plasticity and cognition. In this review, we explore the implication of lipid metabolism in AD, with a special focus on PPARα and its potential role in AD therapy.

The Novel Role of PPAR Alpha in the Brain: Promising Target in Therapy of Alzheimer's Disease and Other Neurodegenerative Disorders

Peroxisome proliferator activated receptor alpha (PPAR-α) belongs to the family of ligand-regulated nuclear receptors (PPARs). These receptors after heterodimerization with retinoid X receptor (RXR) bind in promotor of target genes to PPAR response elements (PPREs) and act as a potent transcription factors. PPAR-α and other receptors from this family, such as PPAR-β/δ and PPAR-γ are expressed in the brain and other organs and play a significant role in oxidative stress, energy homeostasis, mitochondrial fatty acids metabolism and inflammation. PPAR-α takes part in regulation of genes coding proteins that are involved in glutamate homeostasis and cholinergic/dopaminergic signaling in the brain. Moreover, PPAR-α regulates expression of genes coding enzymes engaged in amyloid precursor protein (APP) metabolism. It activates gene coding of α secretase, which is responsible for non-amyloidogenic pathway of APP degradation. It also down regulates β secretase (BACE-1), the main enzyme responsible for amyloid beta (Aβ) peptide release in Alzheimer Diseases (AD). In AD brain expression of genes of PPAR-α and PPAR-γ coactivator-1 alpha (PGC-1α) is significantly decreased. PPARs are altered not only in AD but in other neurodegenerative/neurodevelopmental and psychiatric disorder. PPAR-α downregulation may decrease anti-oxidative and anti-inflammatory processes and could be responsible for the alteration of fatty acid transport, lipid metabolism and disturbances of mitochondria function in the brain of AD patients. Specific activators of PPAR-α may be important for improvement of brain cells metabolism and cognitive function in neurodegenerative and neurodevelopmental disorders.

Association between PPARs Gene Functional Polymorphisms and Ischemic Stroke in Chinese Uyghur Population

PPARγ and PPARα belong to a receptor family of ligand-activated transcription factors involved in the regulation of inflammation, cellular glucose uptake, protection against atherosclerosis and endothelial cell function. Through these effects, they might be involved with the ischemic stroke (IS). We recruited 100 IS patients diagnosed by CTs or/and magnetic resonance imaging (MRI) and 100 normal healthy controls from Chinese Uyghur Population to assess the nature of the functional polymorphisms of PPARs and any links with IS in this unique population which has 60% European ancestry and 40% East Asian ancestry. We found that the Ala allele of the PPARγ Pro12Ala polymorphism was more common in controls than IS subjects (P = 0.008, corrected for multiple testing) in the Uyghur Population. Pro/Ala carriage may be associated with a decreased risk of IS in Uyghurs (OR 0.542, 95% CI 0.346-0.850). Additionally, the 162Val allele frequency at the DNA-binding region of PPARα was extremely rare in Chinese Uguhur IS patients and controls. Our population and ethnic-based study demonstrates that the 162Val allele frequency was extremely low in the Chinese Uyghur Population different from Some European and African populations and the PPARγ 12 Pro/Ala resulting in an amino acid exchange in N-terminal sequence may be an independent protective factor for IS in the Chinese Uyghur Population.

PPARs and Energy Metabolism Adaptation during Neurogenesis and Neuronal Maturation

Peroxisome proliferator activated receptors (PPARs) are a class of ligand-activated transcription factors, belonging to the superfamily of receptors for steroid and thyroid hormones, retinoids, and vitamin D. PPARs control the expression of several genes connected with carbohydrate and lipid metabolism, and it has been demonstrated that PPARs play important roles in determining neural stem cell (NSC) fate. Lipogenesis and aerobic glycolysis support the rapid proliferation during neurogenesis, and specific roles for PPARs in the control of different phases of neurogenesis have been demonstrated. Understanding the changes in metabolism during neuronal differentiation is important in the context of stem cell research, neurodegenerative diseases, and regenerative medicine. In this review, we will discuss pivotal evidence that supports the role of PPARs in energy metabolism alterations during neuronal maturation and neurodegenerative disorders.

Therapeutic Effects of PPAR α on Neuronal Death and Microvascular Impairment

Peroxisome-proliferator activated receptor-alpha (PPARα) is a broadly expressed nuclear hormone receptor and is a transcription factor for diverse target genes possessing a PPAR response element (PPRE) in the promoter region. The PPRE is highly conserved, and PPARs thus regulate transcription of an extensive array of target genes involved in energy metabolism, vascular function, oxidative stress, inflammation, and many other biological processes. PPARα has potent protective effects against neuronal cell death and microvascular impairment, which have been attributed in part to its antioxidant and anti-inflammatory properties. Here we discuss PPARα's effects in neurodegenerative and microvascular diseases and also recent clinical findings that identified therapeutic effects of a PPARα agonist in diabetic microvascular complications.

PPARα signaling in the hippocampus: crosstalk between fat and memory

Major functions of the hippocampus are to generate, organize and store memory. This is a complex process, which is orchestrated by a group of molecules, called plasticity-related molecules. To control these various plasticity-related molecules at the transcriptional level, we have been endowed with cAMP response element-binding protein (CREB), also known as a master regulator of memory. Interestingly, we have seen that this master regulator is regulated at the transcriptional level in the hippocampus by peroxisome proliferator-activated receptor α (PPARα), a nuclear hormone receptor family transcription factor that is known to control the metabolism of fatty acids in the liver, underlying a possible crosstalk between fat and memory. Although liver PPARα does not directly control hippocampal CREB, this opens up an important possibility to improve hippocampal functions and to be resistant to memory loss by PPARα ligands and maintaining normal levels of PPARα in the hippocampus.

Interaction of insulin and PPAR-α genes in Alzheimer's disease: the Epistasis Project

Altered glucose metabolism has been described in Alzheimer's disease (AD). We re-investigated the interaction of the insulin (INS) and the peroxisome proliferator-activated receptor alpha (PPARA) genes in AD risk in the Epistasis Project, including 1,757 AD cases and 6,294 controls. Allele frequencies of both SNPs (PPARA L162V, INS intron 0 A/T) differed between Northern Europeans and Northern Spanish. The PPARA 162LL genotype increased AD risk in Northern Europeans (p = 0.04), but not in Northern Spanish (p = 0.2). There was no association of the INS intron 0 TT genotype with AD. We observed an interaction on AD risk between PPARA 162LL and INS intron 0 TT genotypes in Northern Europeans (Synergy factor 2.5, p = 0.016), but not in Northern Spanish. We suggest that dysregulation of glucose metabolism contributes to the development of AD and might be due in part to genetic variations in INS and PPARA and their interaction especially in Northern Europeans.

The role of environmental exposures in neurodegeneration and neurodegenerative diseases

Neurodegeneration describes the loss of neuronal structure and function. Numerous neurodegenerative diseases are associated with neurodegeneration. Many are rare and stem from purely genetic causes. However, the prevalence of major neurodegenerative diseases is increasing with improvements in treating major diseases such as cancers and cardiovascular diseases, resulting in an aging population. The neurological consequences of neurodegeneration in patients can have devastating effects on mental and physical functioning. The causes of most cases of prevalent neurodegenerative diseases are unknown. The role of neurotoxicant exposures in neurodegenerative disease has long been suspected, with much effort devoted to identifying causative agents. However, causative factors for a significant number of cases have yet to be identified. In this review, the role of environmental neurotoxicant exposures on neurodegeneration in selected major neurodegenerative diseases is discussed. Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis were chosen because of available data on environmental influences. The special sensitivity the nervous system exhibits to toxicant exposure and unifying mechanisms of neurodegeneration are explored.

PPARα polymorphisms as risk factors for dyslipidemia in a Brazilian population

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor α is a nuclear receptor involved in the regulation of several biochemical pathways. Polymorphisms within its gene have been associated with several metabolic traits. We aimed to investigate the association of L162V and Intron 7G>C polymorphisms with serum level markers and common morbidities affecting an older adult/elderly cohort from Cuiaba City, Mato Grosso State, Brazil, as well as to compare the results with a previously studied population from São Paulo City, Brazil.

METHODS AND RESULTS

The studied population consisted of 570 subjects from Cuiaba City, Brazil, who were subjected to clinical interviews and blood collection for laboratory examinations and DNA extraction. Dyslipidemia was defined when participants were taking oral hypolipemiants or those with total cholesterol above 200mg/dL, HDL-c below 40 mg/dL, LDL-c above 130 mg/dL and TG above 150 mg/dL. Restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) was used for polymorphism genotyping. Individual polymorphism and haplotype data were available for analyses. In the studied sample, allele frequencies were 0.052 and 0.292 for 162V and Intron 7C, respectively. In brief, 162V allele was associated with dyslipidemia (p=0.025), and after correction for alcohol consumption and waist-to-rip ratio, a tendency of association could still be observed (p=0.050). In addition, Intron 7C allele was associated with dyslipidemia even after correction for the same variables (p=0.029). When compared to our previous study from São Paulo, we found some divergences regarding these results, which may be explained by differences between the two populations. Haplotype association analyses revealed an association between L/C haplotype and dyslipidemia (p=0.021) and between V/C haplotype and lower LDL-c levels when compared to L/G haplotype (p=0.044).

CONCLUSION

These results may help to clarify the role of PPARα gene in lipid and lipoprotein metabolism and the evaluation of its polymorphisms and haplotypes as being characterized as genetic risk factors for metabolic disturbances.

Plasma n-3 fatty acid response to an n-3 fatty acid supplement is modulated by apoE ɛ4 but not by the common PPAR-α L162V polymorphism in men

The risk of Alzheimer's disease is increased for carriers of apoE4 (E4) or the PPAR-α L162V polymorphism (L162V), but it is decreased in fish and seafood consumers. The link between high fish intake and reduced risk of cognitive decline in the elderly appears not to hold in carriers of E4, possibly because better cognition is linked to EPA+DHA in the blood, but only in non-carriers of E4. As yet, no such studies exist in carriers of L162V. Our objective was to determine whether the plasma fatty acid response to a dietary supplement of EPA+DHA was altered in carriers of L162V and/or E4. This was an add-on project; in the original study, men were selected based on whether or not they were carriers of L162V (n 14 per group). E4 status was determined afterwards. All subjects received an EPA+DHA supplement for 6 weeks. L162V polymorphism did not interact with the supplement in a way to alter EPA and DHA incorporation into plasma lipids. However, when the groups were separated based on the presence of E4, baseline EPA and DHA in plasma TAG were 67 and 60 % higher, respectively, in E4 carriers. After the supplementation, there were significant gene × diet interactions in which only non-carriers had increased EPA and DHA in plasma NEFA and TAG, respectively.

Fatty acid amide hydrolase (FAAH) inhibition enhances memory acquisition through activation of PPAR-alpha nuclear receptors

Inhibitors of fatty acid amide hydrolase (FAAH) increase endogenous levels of anandamide (a cannabinoid CB(1)-receptor ligand) and oleoylethanolamide and palmitoylethanolamide (OEA and PEA, ligands for alpha-type peroxisome proliferator-activated nuclear receptors, PPAR-alpha) when and where they are naturally released in the brain. Using a passive-avoidance task in rats, we found that memory acquisition was enhanced by the FAAH inhibitor URB597 or by the PPAR-alpha agonist WY14643, and these enhancements were blocked by the PPAR-alpha antagonist MK886. These findings demonstrate novel mechanisms for memory enhancement by activation of PPAR-alpha, either directly by administering a PPAR-alpha agonist or indirectly by administering a FAAH inhibitor.

The PPAR-α gene in Alzheimer's disease: Lack of replication of earlier association

Recently, a single nucleotide polymorphism (SNP, rs1800206) in the peroxisome proliferator-activated receptor alpha (PPAR-alpha) gene has been proposed to be associated with Alzheimer's disease (AD). To verify this finding, we analyzed the PPAR-alpha SNP in 461 patients with AD and 1395 controls. In subgroups, PPAR-alpha gene data could be investigated in relation to biochemical and neuropathological markers for AD. We found no significant differences in genotype or allele distributions between AD patients and controls. None of the PPAR-alpha gene variants influenced markers for AD.

Molecular mechanism of PPAR in the regulation of age-related inflammation

Evidence from many recent studies has linked uncontrolled inflammatory processes to aging and aging-related diseases. Decreased a nuclear receptor subfamily of transcription factors, peroxisome proliferator-activated receptors (PPARs) activity is closely associated with increased levels of inflammatory mediators during the aging process. The anti-inflammatory action of PPARs is substantiated by both in vitro and in vivo studies that signify the importance of PPARs as major players in the pathogenesis of many inflammatory diseases. In this review, we highlight the molecular mechanisms and roles of PPARalpha, gamma in regulation of age-related inflammation. By understanding these current findings of PPARs, we open up the possibility of developing new therapeutic agents that modulate these nuclear receptors to control various inflammatory diseases such as atherosclerosis, vascular diseases, Alzheimer's disease, and cancer.

The peroxisome proliferator-activated receptor gamma (PPAR-γ2) Pro12Ala polymorphism is associated with higher risk for Alzheimer's disease in octogenarians

Recent observations support the hypothesis that inflammatory processes at the brain level may contribute to the pathogenesis of Alzheimer's disease (AD). Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is involved in such processes, so we thought it interesting to study the Pro12Ala polymorphism in exon 2 of the gene in a sample of late-onset AD patients. We found that Ala genotypes were significantly overrepresented among octogenarian patients compared to controls (p=0.034). Using logistic regression we observed that carrying the Ala allele significantly increased by nearly two-fold the risk of developing AD in subjects 80 years or older (OR=1.98; 95% CI 1.03-3.80, p=0.04). Though this difference was borderline significant after correction for multiple comparisons, our results suggest a possible involvement of the PPAR-gamma gene in susceptibility to late-onset AD in octogenarians.

Stearic acid protects primary cultured cortical neurons against oxidative stress

AIM

To observe the effects of stearic acid against oxidative stress in primary cultured cortical neurons.

METHODS

Cortical neurons were exposed to glutamate, hydrogen peroxide (H2O2), or NaN3 insult in the presence or absence of stearic acid. Cell viability of cortical neurons was determined by MTT assay and LDH release. Endogenous antioxidant enzymes activity[superoxide dismutases (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT)] and lipid peroxidation in cultured cortical neurons were evaluated using commercial kits. {3-[1(p-chlorobenzyl)- 5-(isopropyl)-3-t-butylthiondol-2-yl]-2,2-dimethylpropanoic acid, Na} [MK886; 5 micromol/L; a noncompetitive inhibitor of proliferator-activated receptor (PPAR) alpha], bisphenol A diglycidyl ether (BADGE; 100 micromol/L; an antagonist of PPAR gamma), and cycloheximide (CHX; 30 micromol/L, an inhibitor of protein synthesis) were tested for their effects on the neuroprotection afforded by stearic acid. Western blotting was used to determine the PPAR gamma protein level in cortical neurons.

RESULTS

Stearic acid dose-dependently protected cortical neurons against glutamate or H2O2 injury and increased glutamate uptake in cultured neurons. This protection was concomitant to the inhibition of lipid peroxidation and to the promotion activity of Cu/Zn SOD and CAT in cultured cortical neurons. Its neuroprotective effects were completely blocked by BADGE and CHX. After incubation with H2O2 for 24 h, the expression of the PPAR gamma protein decreased significantly (P<0.05), and the inhibitory effect of H2O2 on the expression of PPAR gamma can be attenuated by stearic acid.

CONCLUSION

Stearic acid can protect cortical neurons against oxidative stress by boosting the internal antioxidant enzymes. Its neuroprotective effect may be mainly mediated by the activation of PPAR gamma and new protein synthesis in cortical neurons.

Neuroprotective effects of arachidonic acid against oxidative stress on rat hippocampal slices

Arachidonic acid (AA), 5,8,11,14-eicosateraenoic acid is abundant, active and necessary in the human body. In the present study, we reported the neuroprotective effects and mechanism of arachidonic acid on hippocampal slices insulted by glutamate, NaN(3) or H(2)O(2)in vitro. Different types of models of brain injury in vitro were developed by 1mM glutamate, 10mM NaN(3) or 2mM H(2)O(2). After 30 min of preincubation with arachidonic acid or linoleic acid, hippocampal slices were subjected to glutamate, NaN(3) or H(2)O(2), then the tissue activities were evaluated by using the 2,3,5-triphenyltetrazolium chloride method. Endogenous antioxidant enzymes activities (SOD, GSH-PX and catalase) in hippocampal slices were evaluated during the course of incubation. MK886 (5 microM; a noncompetitive inhibitor of proliferator-activated receptor [PPAR]alpha), BADGE (bisphenol A diglycidyl ether; 100 microM; an antagonist of PPARgamma) and cycloheximide (CHX; 30 microM; an inhibitor of protein synthesis) were tested for their effects on the neuroprotection afforded by arachidonic acid. Population spikes were recorded in randomly selected hippocapal slices. Arachidonic acid (1-10 microM) dose dependently protected hippocampal slices from glutamate and H(2)O(2) injury (P<0.01), and arachidonic acid (10 microM) can significantly improve the activities of Cu/Zn-SOD in hippocampal slices after 1h incubation. In addition, 10 microM arachidonic acid significantly increased the activity of Mn-SOD and catalase, and decreased the activities of Cu/Zn-SOD to control value after 3h incubation. These secondary changes of SOD during incubation can be reversed by indomethacine (10 microM; a nonspecific cyclooxygenase inhibitor) or AA 861 (20 microM; a 5-lipoxygenase inhibitor). Its neuroprotective effect was completely abolished by BADGE and CHX. These observations reveal that arachidonic acid can defense against oxidative stress by boosting the internal antioxidant system of hippocampal slices. Its neuroprotective effect may be mainly mediated by the activation of PPARgamma and synthesis of new protein in tissue.

Therapy Insight: type 2 diabetes mellitus and the risk of late-onset Alzheimer's disease

A number of well-designed epidemiological studies have linked type 2 diabetes mellitus (T2DM) with an increased risk of Alzheimer's disease (AD). Several mechanisms could help to explain this proposed link, including insulin and insulin resistance, inflammatory cytokines, and oxidative stress. Obesity or physical inactivity might also influence AD through effects on hypertension, insulin sensitivity or inflammation. Typical AD pathology, such as amyloid-beta deposits, might be exacerbated by insulin dysregulation, T2DM itself, or microvascular disease that is a consequence of T2DM. T2DM patients are not routinely evaluated for cognitive outcomes, and cognitive impairment in T2DM is rarely treated. Similarly, AD patients are not routinely evaluated for T2DM or hyperinsulinemia. Current treatments for AD have only modest benefits, and several drugs that target metabolic and inflammatory pathways are being evaluated, most notably the statins, which reduce LDL and inflammation but might not influence amyloid- deposition, an important precursor for AD. Although some evidence supports a potentially important role for peroxisome proliferative activated receptor agonists such as glitazones, at present there are no published randomized clinical trials in AD patients of any drugs that target insulin or insulin resistance. Clinical implications of the T2DM-AD link include cognitive evaluations of patients with T2DM, and potential benefits for such patients through treatment with statins or diabetes drugs that target insulin.

PPARD haplotype influences cholesterol metabolism but is no risk factor of Alzheimer's disease

Cholesterol metabolism is involved in Alzheimer's disease (AD) pathogenesis: increased cholesterol blood levels are detected in AD patients, and treatment with statins reduces the risk of AD. The peroxisome proliferator-activated receptor delta protein (PPARdelta), is a member of the steroid hormone super family of ligand-inducible transcription factors, and is of major relevance in lipid and cholesterol metabolism. We investigated three frequent polymorphisms located in exons 4 (rs2016520) and 9 (rs3734254 and rs9794) of the PPARdelta gene (PPARD) for their putative influence on the risk of AD and on plasma levels of cholesterol, 24S-hydroxycholesterol and 27-hydroxycholesterol. The study population consisted of 167 AD patients (mean age: 74.27+/-9.37 years; female 78.6%) and 194 controls (mean age: 73.26+/-8.37 years; female 57.2%). Haplotype analysis was perfomed, however, we did not find PPARD haplotypes to influence the risk of AD. In contrast to these results, a two marker haplotype consisting of rs2016520 and rs9794 in AD patients showed a significant effect on the relative plasma levels of 24S-hydroxycholesterol (carriers: 32.1+/-2.8ng/mg; non-carriers: 40.3+/-1.4ng/mg; p=0.016) and 27-hydroxycholesterol (carriers: 40.8+/-7.7ng/mg; non-carriers: 58.6+/-2.3ng/mg; p=0.002) but not in non-demented controls. Our results suggest that PPARD haplotypes might influence levels of cholesterol metabolites in AD patients, but act not as risk factors of AD.

Novel therapeutic opportunities for Alzheimer's disease: focus on nonsteroidal anti-inflammatory drugs

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder with dementia in the elderly. The AD brain pathology is characterized by deposits of amyloid-beta (Abeta) peptides and neurofibrillary tangles but also (among other aspects) by signs of a chronic inflammatory process. Epidemiological studies have shown that long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) reduces the risk of developing AD and delays its onset. Classical targets of NSAIDs include cycloxygenase, nuclear factor kappaB, and peroxisome proliferator-activated receptors. Modulation of these pathways, all of which have been implicated in AD pathogenesis, could explain the NSAID effect on AD progression. However, recent studies indicate that a subset of NSAIDs such as ibuprofen, indomethacin, and flurbiprofen may have direct Abeta-lowering properties in cell cultures as well as transgenic models of AD-like amyloidosis. A renewed interest in the old and a discovery of new pharmacological properties of these drugs are providing vital insight for future clinical trials. In this review we will summarize how the combination of traditional (anti-inflammatory) and new (anti-amyloidogenic) properties of some NSAIDs is providing unprecedented opportunities for drug discovery and could potentially result in novel therapeutic approaches for the treatment of AD.

Contribution of inflammatory processes to Alzheimer's disease: molecular mechanisms

There is compelling evidence that Alzheimer's disease (AD) amyloid-beta (Abeta) deposition is associated with a local inflammatory response, which is initiated by the activation of microglia and the recruitment of astrocytes. These cells secrete a number of cytokines and neurotoxic products that may contribute to neuronal degeneration and cell death. It has been documented that long-term intake of non-steroidal anti-inflammatory drugs (NSAIDs) decrease the risk for developing AD and delay the onset of the disease. The mechanism behind these NSAIDs is still controversial and several hypotheses have been raised, including changes in the amyloid precursor protein (APP) metabolism, in Abeta aggregation and a decrease in inflammatory mediators. Recently, it was proposed that some NSAIDs might activate the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma belongs to a family of nuclear receptors that are able to regulate the transcription of pro-inflammatory molecules, such as iNOS. The activation of PPAR-gamma has been recently reported to reduce Abeta levels in cell culture and AD animal models. The implication of PPAR-gamma in the control of Abeta-induced inflammation suggests a new target for AD therapy and emphasize the contribution of neuroinflammatory mechanisms to the pathogenesis of AD.

Neuroprotective effects of stearic acid against toxicity of oxygen/glucose deprivation or glutamate on rat cortical or hippocampal slices

AIM

To observe the effects of stearic acid, a long-chain saturated fatty acid consisting of 18 carbon atoms, on brain (cortical or hippocampal) slices insulted by oxygen-glucose deprivation (OGD), glutamate or sodium azide (NaN3) in vitro.

METHODS

The activities of hippocampal slices were monitored by population spikes recorded in the CA1 region. In vitro injury models of brain slice were induced by 10 min of OGD, 1 mmol/L glutamate or 10 mmol/L NaN3. After 30 min of pre-incubation with stearic acid (3-30 micromol/L), brain slices (cortical or hippocampal) were subjected to OGD, glutamate or NaN3, and the tissue activities were evaluated by using the 2,3,5-triphenyltetrazolium chloride method. MK886 [5 mmol/L; a noncompetitive inhibitor of proliferator-activated receptor (PPAR-alpha)] or BADGE (bisphenol A diglycidyl ether; 100 micromol/L; an antagonist of PPAR-gamma) were tested for their effects on the neuroprotection afforded by stearic acid.

RESULTS

Viability of brain slices was not changed significantly after direct incubation with stearic acid. OGD, glutamate and NaN3 injury significantly decreased the viability of brain slices. Stearic acid (3-30 micromol/L) dose-dependently protected brain slices from OGD and glutamate injury but not from NaN3 injury, and its neuroprotective effect was completely abolished by BADGE.

CONCLUSION

Stearic acid can protect brain slices (cortical or hippocampal) against injury induced by OGD or glutamate. Its neuroprotective effect may be mainly mediated by the activation of PPAR-gamma.

Influence of peroxisome proliferator-activated receptor γ gene polymorphism on 24S-hydroxycholesterol levels in Alzheimer’s patients

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear hormone receptor, that is involved in lipid and glucose metabolism, which both seem to influence the risk of Alzheimer's disease (AD). 24S-Hydroxycholesterol is the major cholesterol elimination product of the brain and plasma and CSF 24S-hydroxycholesterol levels are altered in patients with neurodegenerative diseases. We investigated the effect of the common Pro12Ala variant of the PPARgamma gene on plasma cholesterol levels and 24S-hydroxycholesterol/ cholesterol ratios in 124 AD patients and 77 healthy controls. Furthermore, the influence of PPARgamma polymorphism on the risk of AD in 247 AD patients and 324 healthy controls was investigated. We found that PPARgamma Pro12Ala polymorphism influenced plasma 24S-hydroxycholesterol/ cholesterol ratios in AD patients in that carriers of the Ala allele presented with higher ratios than homozygote carriers of the Pro-allele. PPARgamma polymorphism did not influence the risk of AD. These results might point to an influence of PPARgamma Pro12Ala polymorphism on the elimination of 24S-hydroxycholesterol.