J. Neurochem.(2010)112, 1415–1430. Alzheimer’s disease (AD) is an age‐related neurodegenerative disease increasingly recognized as one of the most important medical problems affecting the elderly. Although a number of drugs, including several cholinesterase inhibitors and an NMDA receptor antagonist, have been approved for use, they have been shown to produce diverse side effects and yield relatively modest benefits. To overcome these limitations of current therapeutics for AD, extensive research and development are underway to identify drugs that are effective and free of undesirable side effects. Certain naturally occurring dietary polyphenolic phytochemicals have received considerable recent attention as alternative candidates for AD therapy. In particular, curcumin, resveratrol, and green tea catechins have been suggested to have the potential to prevent AD because of their anti‐amyloidogenic, anti‐oxidative, and anti‐inflammatory properties. These polyphenolic phytochemicals also activate adaptive cellular stress responses, called ‘neurohormesis’, and suppress disease processes. In this commentary, we describe the amyloid‐β‐induced pathogenesis of AD, and summarize the intracellular and molecular targets of selected dietary phytochemicals that might slow the progression of AD.

The receptor for advanced glycation end products (RAGE) has been reported to have a pivotal role in the pathogenesis of Alzheimer’s disease (AD). This study investigated RAGE levels in the hippocampus and cortex of a triple transgenic mouse model of AD (3xTg-AD) using western blotting and immunohistochemical double-labeling to assess cellular localization. Analysis of western blots showed that there were no differences in the hippocampal and cortical RAGE levels in 10-month-old adult 3xTg-AD mice, but significant increases in RAGE expression were found in the 22- to 24-month-old aged 3xTg-AD mice compared with those of age-matched controls. RAGE-positive immunoreactivity was observed primarily in neurons of aged 3xTg-AD mice with very little labeling in non-neuronal cells, with the notable exception of RAGE presence in astrocytes in the hippocampal area CA1. In addition, RAGE signals were co-localized with the intracellular amyloid precursor protein (APP)/amyloid beta (Aβ) but not with the extracellular APP/Aβ. In aged 3xTg-AD mice, expression of human tau was observed in the hippocampal area CA1 and co-localized with RAGE signals. The increased presence of RAGE in the 3xTg-AD animal model showing critical aspects of AD neuropathology indicates that RAGE may contribute to cellular dysfunction in the AD brain.

To investigate the inhibitory effect of cocoa polyphenol extract (CPE) on adipogenesis and obesity along with its mechanism of action. 3T3-L1 preadipocytes were cultured with isobutylmethylxanthine, dexamethasone and insulin (MDI), and male C57BL/6N mice (N=44) were fed a high-fat diet (HFD) for 5 weeks with or without CPE. CPE at 100 or 200 μg ml⁻¹ inhibited MDI-induced lipid accumulation without diminishing cell viability. In particular, CPE reduced the protein expression levels of PPARγ and CEBPα, and blocked mitotic clonal expansion (MCE) of preadipocytes by reducing proliferating signaling pathways. This in turn attenuates lipid accumulation during the differentiation of 3T3-L1 preadipocytes. CPE effectively suppressed MDI-induced phosphorylation of extracellular signal-regulated kinase (ERK) and Akt, and their downstream signals. We then examined whether CPE regulates insulin receptor (IR), a common upstream regulator of ERK and Akt. We found that although CPE does not affect the protein expression level of IR, it significantly inhibits the activity of IR kinase via direct binding. Collectively, the results suggested that CPE, a direct inhibitor of IR kinase activity, inhibits cellular differentiation and lipid accumulation in 3T3-L1 preadipocytes. Consistently, CPE attenuated HFD-induced body weight gain and fat accumulation in obese mice fed with a HFD. We also found that HFD-induced increased fasting glucose levels remained unaffected by CPE. This study demonstrates that CPE inhibits IR kinase activity and its proliferative downstream signaling markers, such as ERK and Akt, in 3T3-L1 preadipocytes, and also prevents the development of obesity in mice fed with a HFD.

Cadmium is a well-known carcinogenic and immunotoxic metal commonly found in cigarette smoke and industrial effluent. An altered intracellular calcium ([Ca²⁺]_i) level has been implicated in the pathophysiology of immune dysfunction. The present study was designed to determine the possible involvement of calcium (Ca²⁺) and mitogen-activated protein kinases (MAPKs) signaling pathways on cadmium-induced cell death in J774A.1 murine macrophage cells. Cadmium caused a low-amplitude [Ca²⁺]_i elevation at 20 μM and rapid and high-amplitude [Ca²⁺]_i elevation at 500 μM. Exposure to cadmium dose-dependently induced phosphorylation of c-Jun NH₂-terminal kinase (JNK) and deactivated p38 MAPK. Use of the selective JNK inhibitor SP600125 suggested that activation of JNK is pro-apoptotic and pro-necrotic. Buffering of the calcium response with 1,2-bis-(2-aminophenoxy)-ethane-N,N,N′,N′-tetraacetic acid tetrakis (acetoxy-methyl) ester (BAPTA-AM) and ethylene glycol-bis-(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) completely blocked cadmium-induced apoptotic response. The pretreatment of cells with BAPTA-AM and EGTA suppressed the cadmium-induced cell injury, including growth arrest, mitochondrial activity impairment, and necrosis, and it also recovered the cadmium-altered JNK and p38 MAPK activity. Chelating [Ca²⁺]_i also reversed cadmium-induced hydrogen peroxide generation, suggesting that production of reactive oxygen species (ROS) is related to [Ca²⁺]_i. The present study showed that cadmium induces a [Ca²⁺]_i-ROS-JNK-caspase-3 signaling pathway leading to apoptosis. Furthermore, cadmium-induced [Ca²⁺]_i regulates phosphorylation/dephosphorylation of JNK and p38, and it modulates signal transduction pathways to proliferation, mitochondrial activity, and necrosis.