Current Pharmaceutical Design - Volume 20, Issue 15, 2014

The sporadic, late onset form of Alzheimer's disease (AD) shares pathological hallmarks with the familial form; however, no clear reason for increased β-amyloid (Aβ) generation has been found in the former. It has long been speculated that the late onset form of AD is caused by reduced degradation and/or clearance of Aβ. Indeed, both intracellular degradation systems, the proteasomal and lysosomal systems, have been shown to be defective in AD. Reduced proteasome activity increases levels of intracellular and secreted Aβ. Furthermore, accumulation of improperly degraded Aβ in the lysosomes causes lysosomal disruption and cell death. We recently showed that oligomeric Aβ can be transmitted from one neuron to another, which causes neurotoxicity. In both the donating and receiving cells, Aβ accumulates in the endo-lysosomal compartment. It is possible that ineffective degradation of Aβ causes its transfer to neighboring neurons, thereby spreading AD pathology. This review summarizes the data underlying the idea of reduced Aβ clearance and subsequent Aβ spread in AD, and also suggests new therapeutic methods, which are aimed at targeting the degradation systems and synaptic transfer. By enhancing degradation of intracellular accumulated Aβ, it can be possible to remove it and avoid Aβ-induced neurodegeneration without disturbing the endogenously important pool of secreted Aβ. Additionally, drugs targeted to inhibit the spread of intracellular toxic Aβ aggregates may also be useful in stopping the progression of pathology, without affecting the level of Aβ that normally occurs in the brain.

Despite decades of research, therapy for diseases caused by abnormal protein folding and aggregation (amyloidoses) is limited to treatment of symptoms and provides only temporary and moderate relief to sufferers. The failure in developing successful diseasemodifying drugs for amyloidoses stems from the nature of the targets for such drugs – primarily oligomers of amyloidogenic proteins, which are distinct from traditional targets, such as enzymes or receptors. The oligomers are metastable, do not have well-defined structures, and exist in dynamically changing mixtures. Therefore, inhibiting the formation and toxicity of these oligomers likely will require out-of-the-box thinking and novel strategies. We review here the development of a strategy based on targeting the combination of hydrophobic and electrostatic interactions that are key to the assembly and toxicity of amyloidogenic proteins using lysine (K)-specific “molecular tweezers” (MTs). Our discussion includes a survey of the literature demonstrating the important role of K residues in the assembly and toxicity of amyloidogenic proteins and the development of a lead MT derivative called CLR01, from an inhibitor of protein aggregation in vitro to a drug candidate showing effective amelioration of disease symptoms in animal models of Alzheimer's and Parkinson's diseases.

Alzheimer's disease (AD) is a slowly progressing disease and the evaluation of clinical effects of candidate drugs requires large clinical cohorts as well as long treatment trials. There is a great need for central biomarkers and translatable pre-clinical models to provide early indication of treatment effects. We set out to evaluate the guinea pig as a clinically translatable model looking at Aβ peptides. Our data demonstrate homology between β-amyloid (Aβ) peptide pattern in cerebrospinal fluid (CSF) from human and guinea pig. To further evaluate the model a novel γ-secretase modulator was used. Dose and time response studies confirm the modulatory properties with a statistically significant decrease in relative levels of Aβ1-40, Aβ1-42 and increase in Aβ1-37 already one hour after administration. We suggest that the guinea pig is a compelling pre-clinical model for evaluating and translating central effects on Aβ peptides in CSF after treatment. Further quantitative data are needed to confirm our data together with data from clinical trials in order to back translate and validate our findings.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cerebral accumulation of extracellular amyloid β (Aβ) and neurofibrillary tangles made of hyperphosphorylated tau protein, two main lesions which appear sequentially during the disease progression. In the last decade numerous studies have proposed small soluble aggregates of Aβ, known as oligomers, as the species responsible for synaptic dysfunction, memory loss and neurodegeneration typical of AD. In vitro and in vivo experiments have identified Aβ oligomers as the elements that can alter synaptic function by a reversible mechanism, which gradually becomes permanent when exposure is continuous. Here we show that intracerebroventricular (ICV) injection in mice of a solution containing specifically Aβ1-42 oligomers substantially affects their memory when tested in the novel object recognition task. This acute mouse model enabled us to distinguish whether oligomers were affecting specific phases of the memory processing. A single injection of Aβ1-42 oligomers before memory consolidation abolished information processing, leading to memory impairment, whereas no such effects were observed when the injection was done once the information had been processed, indicating that the oligomers affect memory consolidation rather than retrieval. Beside Aβ1-42, Aβ1-40 oligomers also impaired memory, and both isoforms were antagonized by the anti-Aβ4G8 monoclonal antibody./p This simple and reliable paradigm is useful to investigate the mechanisms through which Aβ oligomers interfere with neuronal processes and to test the efficacy of new therapeutic approaches specifically against these species. We tested several molecules by direct coincubation with Aβ oligomers, ICV injections preceding Aβ oligomers, and the systemic treatment with drugs that cross the blood brain barrier. We also examined the proposed involvement of cellular prion protein as a mediator of the oligomer-induced memory impairment.

The neurodegenerative process that defines Alzheimer’s disease (AD) is initially characterized by synaptic alterations followed by synapse loss and ultimately cell death. Decreased synaptic density that precedes neuronal death is the strongest pathological correlate of cognitive deficits observed in AD. Substantial synapse and neuron loss occur early in disease progression in the entorhinal cortex (EC) and the CA1 region of the hippocampus, when memory deficits become clinically detectable. Mounting evidence suggests that soluble amyloid-β (Aβ) oligomers trigger synapse dysfunction both in vitro and in vivo. However, the neurodegenerative effect of Aβ species observed on neuronal culture or organotypic brain slice culture has been more challenging to mimic in animal models. While most of the transgenic mice that overexpress Aβ show abundant amyloid plaque pathology and early synaptic alterations, these models have been less successful in recapitulating the spatiotemporal pattern of cell loss observed in AD. Recently we developed a novel animal model that revealed the neurodegenerative effect of soluble low-molecular-weight Aβ oligomers in vivo. This new approach may now serve to determine the molecular and cellular mechanisms linking soluble Aβ species to neurodegeneration in animals. In light of the low efficiency of AD therapies based on the amyloid cascade hypothesis, a novel framework, the aging factor cascade hypothesis, is proposed in an attempt to integrate the new data and concepts that emerged from recent research to develop disease modifying therapies.

So far, therapeutics focusing on reducing levels of amyloid beta for treatment of Alzheimer’s disease have not been successful in completing clinical trials to come to market, suggesting the need of a wider perspective and the consideration of novel targets of intervention to slow or halt the progression of this disease. One such target is soluble amyloid beta in oligomeric forms, which have been demonstrated to bind with high affinity to zinc released during synaptic activity. This review considers the interaction of AβO and zinc and the role of zinc in neurotransmission along with possible neurotoxic effects of this interaction. Finally, it also discusses recent experimental data in animal models that have translated into potential treatments for AD based on the modulation of hyperexcitability and zinc homeostasis.

The review examines the multifaceted interactions between cholinergic transmission and beta-amyloid suggesting a continuum in the action of the peptide that at low concentrations (picomolar-low nanomolar) may directly stimulate nicotinic cholinergic receptor while desensitizing them at increasing concentrations (high nanomolar-low micromolar). In addition high beta-amyloid concentrations may reduce the synaptic release of several neurotransmitters, including glutamate, aspartate, GABA, glycine and dopamine, when the release is elicited through cholinergic stimulation but not following depolarization. The effect of beta-amyloid has been observed both in vitro and in vivo in at least three different brain areas (nucleus accumbens, striatum, hippocampus) suggesting that the peptide may exert some general effects even if not all the brain areas have been evaluated. In turn the activation of cholinergic receptors may affect the amyloid precursor protein processing diverting the metabolism toward non-amyloidogenic products. These actions, dissociated from those described in the case of high beta-amyloid concentrations leading to neurotoxic oligomers, may participate to cause dysfunctions in the neurotransmitter activity, in turn leading, at least from a theoretical point of view, to early neuropsychiatric disturbances in the disease. Complexively these observations underscore novel relationships between two main players in Alzheimer's disease pathogenesis that are beta-amyloid and cholinergic transmission. Also emerges the inherent difficulty of targeting beta-amyloid in a context in which the peptide exerts several actions beyond neurotoxicity.

Despite the consolidation of the amyloid hypothesis, the main component of senile plaques in Alzheimer’s disease (AD), recent findings have led to a conceptual shift opening new questions about the potential physiological role of this peptide. In addition, soluble beta amyloid (sBA), in transgenic AD model, resulted to be increased after chronic and acute stress and alterations in cortisol levels have been reported in AD. Impaired hypothalamic pituitary adrenal (HPA) axis has been linked to depressive state and, consistently, we have previously demonstrated that BA is able to provoke depressive-like profile in rats. Here we further analysed the effect of the peptide in behavioural paradigms used to study emotional and cognitive response, by using the passive avoidance task, for cognitive parameters, and the sucrose preference test (SPT), to evaluate anhedonia. Moreover, in order to correlate behavioural with neurochemical and neuroendocrinal data, we investigated the effects of the peptide on noradrenergic system in amygdala (AMY), prefrontal cortex (PFC) and hippocampus (HIPP) along with plasmatic corticosterone and hypothalamic corticotrophin releasing factor (CRF). We found that BAtreated animals showed an impaired memory consolidation of inhibitory avoidance training, while no effect was evident in SPT. These results lead us to hypothesize a different response to stress coping behaviour in BA treated rats. Moreover, BA caused a significant increase in noradrenaline (NA) in PFC and HIPP, while in AMY was decreased. Consistently, we found a significant decrease in plasma corticosterone concentrations in BA-treated rats. Taken together, our data suggest that BA exerts an inhibitory effect on HPA axis activation.

Late-Life Major Depression (LLMD) is a complex heterogeneous disorder that has multiple pathophysiological mechanisms such as medical comorbidity, vascular-related factors and Alzheimer’s disease (AD). There is an association between LLMD and AD, with LLMD possibly being a risk factor for, or early symptom of AD and vascular dementia. Whether depression is an etiologic risk factor for dementia, or part of the dementia prodrome remains controversial. AD has a long prodromal period with the neuropathologic features of the disease preceding the onset of clinical symptoms by as much as 15–20 years. Clinicopathological studies have provided robust support for the importance of Aβ42 in the pathogenesis of AD, but several other risk factors have also been identified. Given the relationship between Aβ42 and AD, a potential relationship between Aβ42 and LLMD would improve the understanding of the association between LLMD and AD. We reviewed 15 studies that analyzed the relationship between soluble Aβ42 and LLMD. For studies looking at plasma and/or cerebrospinal fluid (CSF) levels of Aβ42, the relationship between LLMD and soluble Aβ42 was equivocal, with some studies finding elevated Aβ42 levels associated with LLMD and others finding the opposite, decreased levels of Aβ42 associated with LLMD. It may be that there is poor reliability in the diagnosis of depression in late life, or variability in the criteria and the scales used, or subtypes of depression in late life such as early vs. late onset depression, vascular-related depression, and preclinical/comorbid depression in AD. The different correlations associated with each of these factors would be causing the inconsistent results for soluble Aβ42 levels in LLMD, but it is also possible that these patterns derive from disease stage-dependent differences in the trajectory of CSF Aβ42 during older age, or changes in neuronal activity or the sleep/wake cycle produced by LLMD that influence Aβ42 dynamics.

Tumor cells suffer a metabolic reprogramming which allows them to use metabolic fuels (glucose, glutamine, lipids) through anabolic fates to support their enhanced proliferation and other carcinogenesis-related features. The present review tries to address and summarize the broad and growing information available about this reprogramming, whose pieces, put together, make up a complex scheme that encompasses different complexity scales, from cells to systemic networks.

Metabolism in cancer cells is reprogrammed. Cancer cells largely depend on glycolysis for ATP production. The metabolic alterations in cancer cells facilitate resistance to cell death as well as biosynthesis of nucleotides and lipids, building blocks for growth. The reprogrammed metabolism is increasingly seen as a target in cancer therapy. This review describes the metabolic reprogramming of cancer cells and illustrates how this is related to cell cycle and apoptosis resistance. Is also describes various scenarios for targeting cancer cell metabolism and highlights options for interventions with nutrition and bioactive food components.

Cancer cells are characterized by reprogramming of energy metabolism. Over the last decade, understanding of the metabolic changes that occur in cancer has increased dramatically, with great interest in targeting metabolism for cancer therapy. Pyruvate kinase isoenzyme type M2 (abbreviations: PKM2, M2-PK) plays a key role in modulating glucose metabolism to support cell proliferation. PKM2, like other PK isoforms, catalyzes the last energy-generating step in glycolysis, but is unique in its capacity to be regulated. PKM2 is regulated at several cellular levels, including gene expression, alternative splicing and post-translational modification. In addition, PKM2 is regulated by key metabolic intermediates and interacts with more than twenty different proteins. Hence, this isoenzyme is an important regulator of glycolysis, and additionally functions in other novel roles that have recently emerged. Recent evidence indicates that intervening with the complex regulatory network of PKM2 has severe consequences on tumor cell proliferation, indicating the potential of this enzyme as a target for tumor therapy.

Adenosine monophosphate-activated protein kinase (AMPK) is a key player in maintaining energy homeostasis in response to metabolic stress. Beyond diabetes and metabolic syndrome, there is a growing interest in the therapeutic exploitation of the AMPK pathway in cancer treatment in light of its unique ability to regulate cancer cell proliferation through the reprogramming of cell metabolism. Although many studies support the tumor-suppressive role of AMPK, emerging evidence suggests that the metabolic checkpoint function of AMPK might be overridden by stress or oncogenic signals so that tumor cells use AMPK activation as a survival strategy to gain growth advantage. These findings underscore the complexity in the cellular function of AMPK in maintaining energy homeostasis under physiological versus pathological conditions. Thus, this review aims to provide an overview of recent findings on the functional interplay of AMPK with different cell metabolic and signaling effectors, particularly histone deacetylases, in mediating downstream tumor suppressive or promoting mechanisms in different cell systems. Although AMPK activation inhibits tumor growth by targeting multiple signaling pathways relevant to tumorigenesis, under certain cellular contexts or certain stages of tumor development, AMPK might act as a protective response to metabolic stresses, such as nutrient deprivation, low oxygen, and low pH, or as downstream effectors of oncogenic proteins, including androgen receptor, hypoxia-inducible factor-1α, c-Src, and MYC. Thus, investigations to define at which stage(s) of tumorigenesis and cancer progression or for which genetic aberrations AMPK inhibition might represent a more relevant strategy than AMPK activation for cancer treatment are clearly warranted.

Metabolic reprogramming is a hallmark of cancer. Oncogenic growth signaling regulates glucose, glutamine and lipid metabolism to meet the bioenergetics and biosynthetic demands of rapidly proliferating tumor cells. Emerging evidence indicates that sterol regulatory element-binding protein 1 (SREBP-1), a master transcription factor that controls lipid metabolism, is a critical link between oncogenic signaling and tumor metabolism. We recently demonstrated that SREBP-1 is required for the survival of mutant EGFRcontaining glioblastoma, and that this pro-survival metabolic pathway is mediated, in part, by SREBP-1-dependent upregulation of the fatty acid synthesis and low density lipoprotein (LDL) receptor (LDLR). These results have identified EGFR/PI3K/Akt/SREBP-1 signaling pathway that promotes growth and survival in glioblastoma, and potentially other cancer types. Here, we summarize recent insights in the understanding of cancer lipid metabolism, and discuss the evidence linking SREBP-1 with PI3K/Akt signaling-controlled glycolysis and with Myc-regulated glutaminolysis to lipid metabolism. We also discuss the development of potential drugs targeting the SREBP-1- driven lipid metabolism as anti-cancer agents.

Lysine acetylation plays an essential role in metabolism. Five individual studies have identified that a large number of cellular proteins are potentially acetylated. Notably, almost every enzyme involved in central metabolic pathways such as glycolysis, the TCA cycle, fat acid metabolism, urea cycle and glycogen metabolism, is acetylated in response to nutrition fluctuations. Metabolic reprogramming is a critical hallmark during cancer development. Tumor cells preferentially utilize glycolysis instead of oxidative phosphorylation to produce more lactate and metabolic intermediates even under normal oxygen pressure, which was first noted as the “Warburg Effect”. This review focuses on recent advances in the acetylation regulation of metabolic enzymes involved in the Warburg effect, the dysfunction of acetylation regulation in tumorigenesis and their potential role in cancer metabolism therapy.

Sirtuin 1 (SIRT1) is an NAD+-dependent histone deacetylase which regulates many normal physiological and pathological processes. In addition to its place in cellular energy metabolism, increasing evidence shows a role for SIRT1 in tumorigenesis, wherein it can function as either a tumor promoter or suppressor. Its function in malignancy varies with concentration, cellular location, temporal and spatial distribution, and regulation by upstream and downstream factors. In this mini-review, we present the existing data which implicates SIRT1 in tumorigenesis.

Reprogramming of energy metabolism has recently been added to the list of hallmarks that define cancer. Cellular metabolism plays a central role in cancer initiation and progression to metastatic disease. Genotypic and phenotypic metabolic alterations are seen throughout tumourigenesis, allowing cancer cells to sustain increased rates of proliferation. Furthermore, this shift fuels necessary substrates for nucleotide, protein, and lipid synthesis to support cell growth. Beyond the ‘Warburg effect’, the widely observed increase in the glycolytic processing of glucose in cancer cells, numerous other metabolic changes have been characterized in cancer. Metabolomics provides a valuable platform for the investigation of the metabolic perturbations that occur in different disease states using a systems biology approach to determine metabolic profiles of biological samples. As cell metabolism is a complex network of interdependent pathways, local alterations will have an impact on overall tumor metabolism. In this review, we will highlight particular pathways, including glycolysis, nucleotide biosynthesis, lipid metabolism, and bioenergetics with an eye towards selected metabolic targets that may provide a novel approach to therapeutic development. Specific regulatory factors, including Myc, p53, HIF-1 and mTOR are briefly highlighted, as well as the key signaling pathways that can affect cellular metabolism. To demonstrate the powerful utility of high-throughput metabolite profiling techniques, we present a practical example of the metabolomic profiling of metastatic cells derived from a lung cancer metastasis model.

Despite their different histological and molecular properties, different types of cancers share few essential functional alterations. Some of these cancer hallmarks may easily be studied in in vitro cultures, while others are related to the way in which tumors grow in vivo. According to the systems biology paradigm, complex cellular functions arise as system-level properties from the dynamic interaction of a large number of biomolecules. We previously newly defined four basic cancer cell properties derived from known cancer hallmarks amenable to system-level investigation in cell cultures: enhanced growth, altered response to apoptotic cues, genomic instability and inability to enter senescence following oncogenic signaling. Here we summarize the major properties of enhanced growth that is dependent on metabolism rewiring - in which glucose is mostly used by fermentation while glutamine provides nitrogen and carbon atoms for biosyntheses – and controlled by oncogene signaling. We then briefly review the major drugs used to target signaling pathways in preclinical and clinical studies, whose clinical efficacy is unfortunately severely limited by tumor resistance, substantially due to signaling cross-talk. We present a systems biology roadmap that integrates different types of mathematical models with conventional and post-genomic biomolecular analyses that will provide a deeper mechanistic understanding of the links between metabolism and uncontrolled cancer cell growth. This approach is taken to be instrumental both in unraveling cancer’s first principles and in designing novel drugs able to target one or more control or execution steps of the cancer rewired metabolism, in order to achieve permanent arrest of tumor development.