Bruce Teter

Docosahexaenoic Acid Protects from Dendritic Pathology in an Alzheimer's Disease Mouse Model

Learning and memory depend on dendritic spine actin assembly and docosahexaenoic acid (DHA), an essential n-3 (omega-3) polyunsaturated fatty acid (PFA). High DHA consumption is associated with reduced Alzheimers disease (AD) risk, yet mechanisms and therapeutic potential remain elusive. Here, we report that reduction of dietary n-3 PFA in an AD mouse model resulted in 80%-90% losses of the p85alpha subunit of phosphatidylinositol 3-kinase and the postsynaptic actin-regulating protein drebrin, as in AD brain. The loss of postsynaptic proteins was associated with increased oxidation, without concomitant neuron or presynaptic protein loss. n-3 PFA depletion increased caspase-cleaved actin, which was localized in dendrites ultrastructurally. Treatment of n-3 PFA-restricted mice with DHA protected against these effects and behavioral deficits and increased antiapoptotic BAD phosphorylation. Since n-3 PFAs are essential for p85-mediated CNS insulin signaling and selective protection of postsynaptic proteins, these findings have implications for neurodegenerative diseases where synaptic loss is critical, especially AD.

A diet enriched with the omega-3 fatty acid docosahexaenoic acid reduces amyloid burden in an aged alzheimer mouse model

Epidemiological studies suggest that increased intake of the omega-3 (n-3) polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) is associated with reduced risk of Alzheimers disease (AD). DHA levels are lower in serum and brains of AD patients, which could result from low dietary intake and/or PUFA oxidation. Because effects of DHA on Alzheimer pathogenesis, particularly on amyloidosis, are unknown, we used the APPsw (Tg2576) transgenic mouse model to evaluate the impact of dietary DHA on amyloid precursor protein (APP) processing and amyloid burden. Aged animals (17-19 months old) were placed in one of three groups until 22.5 months of age: control (0.09% DHA), low-DHA (0%), or high-DHA (0.6%) chow. β-Amyloid (Aβ) ELISA of the detergent-insoluble extract of cortical homogenates showed that DHA-enriched diets significantly reduced total Aβ by >70% when compared with low-DHA or control chow diets. Dietary DHA also decreased Aβ42 levels below those seen with control chow. Image analysis of brain sections with an antibody against Aβ (amino acids 1-13) revealed that overall plaque burden was significantly reduced by 40.3%, with the largest reductions (40-50%) in the hippocampus and parietal cortex. DHA modulated APP processing by decreasing both α- and β-APP C-terminal fragment products and full-length APP. BACE1 (β-secretase activity of the β-site APP-cleaving enzyme), ApoE (apolipoprotein E), and transthyretin gene expression were unchanged with the high-DHA diet. Together, these results suggest that dietary DHA could be protective against β-amyloid production, accumulation, and potential downstream toxicity.

Curcumin Structure-Function, Bioavailability, and Efficacy in Models of Neuroinflammation and Alzheimer's Disease

Curcumin can reduce inflammation and neurodegeneration, but its chemical instability and metabolism raise concerns, including whether the more stable metabolite tetrahydrocurcumin (TC) may mediate efficacy. We examined the antioxidant, anti-inflammatory, or anti-amyloidogenic effects of dietary curcumin and TC, either administered chronically to aged Tg2576 APPsw mice or acutely to lipopolysaccharide (LPS)-injected wild-type mice. Despite dramatically higher drug plasma levels after TC compared with curcumin gavage, resulting brain levels of parent compounds were similar, correlating with reduction in LPS-stimulated inducible nitric-oxide synthase, nitrotyrosine, F2 isoprostanes, and carbonyls. In both the acute (LPS) and chronic inflammation (Tg2576), TC and curcumin similarly reduced interleukin-1β. Despite these similarities, only curcumin was effective in reducing amyloid plaque burden, insoluble β-amyloid peptide (Aβ), and carbonyls. TC had no impact on plaques or insoluble Aβ, but both reduced Tris-buffered saline-soluble Aβ and phospho-c-Jun NH2-terminal kinase (JNK). Curcumin but not TC prevented Aβ aggregation. The TC metabolite was detected in brain and plasma from mice chronically fed the parent compound. These data indicate that the dienone bridge present in curcumin, but not in TC, is necessary to reduce plaque deposition and protein oxidation in an Alzheimers model. Nevertheless, TC did reduce neuroinflammation and soluble Aβ, effects that may be attributable to limiting JNK-mediated transcription. Because of its favorable safety profile and the involvement of misfolded proteins, oxidative damage, and inflammation in multiple chronic degenerative diseases, these data relating curcumin dosing to the blood and tissue levels required for efficacy should help translation efforts from multiple successful preclinical models.

Role of p21-activated kinase pathway defects in the cognitive deficits of Alzheimer disease

Defects in dendritic spines are common to several forms of cognitive deficits, including mental retardation and Alzheimer disease. Because mutation of p21-activated kinase (PAK) can lead to mental retardation and because PAK-cofilin signaling is critical in dendritic spine morphogenesis and actin dynamics, we hypothesized that the PAK pathway is involved in synaptic and cognitive deficits in Alzheimer disease. Here, we show that PAK and its activity are markedly reduced in Alzheimer disease and that this is accompanied by reduced and redistributed phosphoPAK, prominent cofilin pathology and downstream loss of the spine actin-regulatory protein drebrin, which cofilin removes from actin. We found that β-amyloid (Aβ) was directly involved in PAK signaling deficits and drebrin loss in Aβ oligomer–treated hippocampal neurons and in the Appswe transgenic mouse model bearing a double mutation leading to higher Aβ production. In addition, pharmacological PAK inhibition in adult mice was sufficient to cause similar cofilin pathology, drebrin loss and memory impairment, consistent with a potential causal role of PAK defects in cognitive deficits in Alzheimer disease.

NEUROPROTECTIVE EFFECTS OF CURCUMIN

Neurodegenerative diseases result in the loss of functional neurons and synapses. Although future stem cell therapies offer some hope, current treatments for most of these diseases are less than adequate and ourbest hope is to prevent these devastating diseases. Neuroprotective approaches work best prior to the initiation of damage, suggesting that some safe and effective prophylaxis would be highly desirable. Curcumin has an outstanding safety profile and a number of pleiotropic actions with potential for neuroprotective efficacy, including anti-inflammatory, antioxidant, and anti-protein-aggregate activities. These can be achieved at submicromolar levels. Curcumins dose-response curves are strongly dose dependent and often biphasic so that in vitro data need to be cautiously interpreted; many effects might not be achievable in target tissues in vivo with oral dosing. However, despite concerns about poor oral bioavailability, curcumin has at least 10 known neuroprotective actions and many of these might be realized in vivo. Indeed, accumulating cell culture and animal model data show that dietary curcumin is a strong candidate for use in the prevention or treatment of major disabling age-related neurodegenerative diseases like Alzheimers, Parkinsons, and stroke. Promising results have already led to ongoing pilot clinical trials.

Insulin-Degrading Enzyme as a Downstream Target of Insulin Receptor Signaling Cascade: Implications for Alzheimer's Disease Intervention

Insulin-degrading enzyme (IDE) is one of the proteins that has been demonstrated to play a key role in degrading β-amyloid (Aβ) monomer in vitro and in vivo, raising the possibility of upregulating IDE as an approach to reduce Aβ. Little is known, however, about the cellular and molecular regulation of IDE protein. Because one of the main functions of IDE is to degrade insulin, we hypothesized that there is a negative feedback mechanism whereby stimulation of insulin receptor-mediated signaling upregulates IDE to prevent chronic activation of the pathway. We show that treatment of primary hippocampal neurons with insulin increased IDE protein levels by ∼25%. Insulin treatment also led to phosphatidylinositol-3 (PI3) kinase activation evidenced by Akt phosphorylation, which was blocked by PI3 kinase inhibitors, wortmannin and LY 294002. Inhibition of PI3 kinase abolished the IDE upregulation by insulin, indicating a cause-effect relationship between insulin signaling and IDE upregulation. Further support for this link was provided by the findings that deficient insulin signaling (decreased PI3 kinase subunit P85) was correlated with reduced IDE in Alzheimers disease (AD) brains and in Tg2576 Swedish amyloid precursor protein transgenic mice fed a safflower oil-enriched (“Bad”) diet used to accelerate pathogenesis. Consistent with IDE function in the degradation of Aβ monomer, the IDE decrease in the Bad diet-fed Tg2576 mice was associated with increased Aβ monomer levels. These in vitro and in vivo analyses validate the use of enhanced CNS insulin signaling as a potential strategy for AD intervention to correct the IDE defects occurring in AD.

Glial fibrillary acidic protein: regulation by hormones, cytokines, and growth factors.

Levels of glial fibrillary acidic protein (GFAP), an astrocyte‐specific intermediate filament protein, are altered during development and aging, GFAP also responds dynamically to neurodegenerative lesions. Changes in GFAP expression can occur at both transcriptional and translational levels. Modulators of GFAP expression include steroids, cytokines, and growth factors. GFAP expression also shows brain region‐specific responses to sex steroids and of astrocyte‐neuronal interactions. The 5′‐upstream sequences of rat, mouse, and human are compared for the presence of response elements that are candidates for transcriptional regulation of GFAP. We propose that the regulation of the GFAP gene has evolved a system of controls that allow integrated responses to neuroendocrine and inflammatory modulators.

Prevention of Alzheimer's disease: Omega-3 fatty acid and phenolic anti-oxidant interventions

Alzheimers disease (AD) and cardiovascular disease (CVD) are syndromes of aging that share analogous lesions and risk factors, involving lipoproteins, oxidative damage and inflammation. Unlike in CVD, in AD, sensitive biomarkers are unknown, and high-risk groups are understudied. To identify potential prevention strategies in AD, we have focused on pre-clinical models (transgenic and amyloid infusion models), testing dietary/lifestyle factors strongly implicated in reducing risk in epidemiological studies. Initially, we reported the impact of non-steroidal anti-inflammatory drugs (NSAIDs), notably ibuprofen, which reduced amyloid accumulation, but suppressed few inflammatory markers and without reducing oxidative damage. Safety concerns with chronic NSAIDs led to a screen of alternative NSAIDs and identification of the phenolic anti-inflammatory/anti-oxidant compound curcumin, the yellow pigment in turmeric that we found targeted multiple AD pathogenic cascades. The dietary omega-3 fatty acid, docosahexaenoic acid (DHA), also limited amyloid, oxidative damage and synaptic and cognitive deficits in a transgenic mouse model. Both DHA and curcumin have favorable safety profiles, epidemiology and efficacy, and may exert general anti-aging benefits (anti-cancer and cardioprotective.).

Antibodies against β-amyloid reduce aβ oligomers, glycogen synthase kinase-3β activation and τ phosphorylation in vivo and in vitro

Although active and passive immunization against the β‐amyloid peptide (Aβ) of amyloid plaque‐bearing transgenic mice markedly reduces amyloid plaque deposition and improves cognition, the mechanisms of neuroprotection and impact on toxic oligomer species are not understood. We demonstrate that compared to control IgG2b, passive immunization with intracerebroventricular (icv) anti‐Aβ (1–15) antibody into the AD HuAPPsw (Tg2576) transgenic mouse model reduced specific oligomeric forms of Aβ, including the dodecamers that correlate with cognitive decline. Interestingly, the reduction of soluble Aβ oligomers, but not insoluble Aβ, significantly correlated with reduced τ phosphorylation by glycogen synthase kinase‐3β (GSK‐3β), a major τ kinase implicated previously in mediating Aβ toxicity. A conformationally‐directed antibody against amyloid oligomers (larger than tetramer) also reduced Aβ oligomer‐induced activation of GSK3β and protected human neuronal SH‐SY5Y cells from Aβ oligomer‐induced neurotoxicity, supporting a role for Aβ oligomers in human τ kinase activation. These data suggest that antibodies that are highly specific for toxic oligomer subspecies may reduce toxicity via reduction of GSK‐3β, which could be an important strategy for Alzheimers disease (AD) therapeutics.

Neuroplasticity in Alzheimer's disease.

Ramon y Cajal proclaimed in 1928 that “once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree.” (Ramon y Cajal, 1928 ). In large part, despite the extensive knowledge gained since then, the latter directive has not yet been achieved by ‘modern’ science. Although we know now that Ramon y Cajals observation on CNS plasticity is largely true (for lower brain and primary cortical structures), there are mechanisms for recovery from CNS injury. These mechanisms, however, may contribute to the vulnerability to neurodegenerative disease. They may also be exploited therapeutically to help alleviate the suffering from neurodegenerative conditions. Published 2002 Wiley‐Liss, Inc.