Spermidine improves fear memory persistence

Polyamines and hormesis: Making sense of a dose response dichotomy

The diverse biological effects of polyamines (putrescine, spermidine and spermine) were reviewed in the context of hormesis in an integrative manner for the first time. The findings illustrate that each of these polyamines commonly induces hormetic dose responses in a wide range of biological models and types of cells for multiple endpoints in numerous plant species and animal models. Plant research emphasized preconditioning experimental studies in which the respective polyamines conferred some protection against the damaging effects of a broad range of environmental stressors such as drought, salinity, cold/heat, heavy metals and UV-damage in an hormetic manner. Polyamine-based animal hormesis studies emphasized biomedical endpoints such as longevity and neuroprotection. These findings have important biological and biomedical implications and should guide experimental designs of low dose investigations.

Molecular mechanism of caloric restriction mimetics-mediated neuroprotection of age-related neurodegenerative diseases: an emerging therapeutic approach

Aging-induced neurodegenerative diseases (NDs) are significantly increasing health problem worldwide. It has been well documented that oxidative stress is one of the potential causes of aging and age-related NDs. There are no drugs for the treatment of NDs, therefore there is an immediate necessity for the development of strategies/treatments either to prevent or cure age-related NDs. Caloric restriction (CR) and intermittent fasting have been considered as effective strategies in increasing the healthspan and lifespan, but it is difficult to adhere to these routines strictly, which has led to the development of calorie restriction mimetics (CRMs). CRMs are natural compounds that provide similar molecular and biochemical effects of CR, and activate autophagy process. CRMs have been reported to regulate redox signaling by enhancing the antioxidant defense systems through activation of the Nrf2 pathway, and inhibiting ROS generation through attenuation of mitochondrial dysfunction. Moreover, CRMs also regulate redox-sensitive signaling pathways such as the PI3K/Akt and MAPK pathways to promote neuronal cell survival. Here, we discuss the neuroprotective effects of various CRMs at molecular and cellular levels during aging of the brain. The CRMs are envisaged to become a cornerstone of the pharmaceutical arsenal against aging and age-related pathologies.

Roles of Rac1-Dependent Intrinsic Forgetting in Memory-Related Brain Disorders: Demon or Angel

Animals are required to handle daily massive amounts of information in an ever-changing environment, and the resulting memories and experiences determine their survival and development, which is critical for adaptive evolution. However, intrinsic forgetting, which actively deletes irrelevant information, is equally important for memory acquisition and consolidation. Recently, it has been shown that Rac1 activity plays a key role in intrinsic forgetting, maintaining the balance of the brain's memory management system in a controlled manner. In addition, dysfunctions of Rac1-dependent intrinsic forgetting may contribute to memory deficits in neurological and neurodegenerative diseases. Here, these new findings will provide insights into the neurobiology of memory and forgetting, pathological mechanisms and potential therapies for brain disorders that alter intrinsic forgetting mechanisms.

Administration of spermidine attenuates concanavalin A-induced liver injury

A previous study revealed that treatment with the anticoagulant heparin attenuated concanavalin A (ConA)-induced liver injury. The administration of spermidine (SPD) increased urokinase-type plasminogen activator (uPA) levels in the serum. uPA is clinically used for the treatment of some thrombotic diseases such as cerebral infarction. Therefore, SPD may attenuate ConA-induced liver injury that is exacerbated by blood coagulation. The present study investigated the effect of SPD on liver injury in mice with autoimmune hepatopathy induced by ConA. A model of liver injury was created by intravenous injection of ConA into mice. SPD was administered in free drinking water and was biochemically and pathologically examined over time. The administration of SPD to ConA-treated mice significantly reduced liver injury. However, SPD treatment upregulated the mRNA expression of TNF-α and IFN-ϒ in the livers of ConA-treated mice. In contrast, the mRNA expression of tissue factor in the livers of SPD-treated mice was decreased after ConA injection. The frequency of lymphocytes and lymphocyte activation were not affected by SPD administration in ConA-treated mice. SPD treatment increased uPA levels in the serum and decreased the level of D-dimer in ConA-treated mice. Moreover, SPD decreased fibrin in the livers of ConA-treated mice. These results indicated that SPD treatment increased anticoagulant ability by increasing of uPA and attenuated ConA-induced liver injury.

The Influence of Orthopedic Surgery on Circulating Metabolite Levels, and their Associations with the Incidence of Postoperative Delirium

The mechanisms underlying the occurrence of postoperative delirium development are unclear and measurement of plasma metabolites may improve understanding of its causes. Participants (n = 54) matched for age and gender were sampled from an observational cohort study investigating postoperative delirium. Participants were ≥65 years without a diagnosis of dementia and presented for primary elective hip or knee arthroplasty. Plasma samples collected pre- and postoperatively were grouped as either control (n = 26, aged: 75.8 ± 5.2) or delirium (n = 28, aged: 76.2 ± 5.7). Widespread changes in plasma metabolite levels occurred following surgery. The only metabolites significantly differing between corresponding control and delirium samples were ornithine and spermine. In delirium cases, ornithine was 17.6% higher preoperatively, and spermine was 12.0% higher postoperatively. Changes were not associated with various perioperative factors. In binary logistic regression modeling, these two metabolites did not confer a significantly increased risk of delirium. These findings support the hypothesis that disturbed polyamine metabolism is an underlying factor in delirium that warrants further investigation.

The Role of Polyamines in the Mechanisms of Cognitive Impairment

Abstract—As the population ages, age-related cognitive impairments are becoming an increasingly pressing problem. Currently, the role of polyamines (putrescine, spermidine, and spermine) in the pathogenesis of cognitive impairments of various origin is actively discussed. It was shown that the content of polyamines in the brain tissue decreases with age. Exogenous administration of polyamines makes it possible to avoid cognitive impairment and/or influence the pathogenetic processes associated with disease progression. There are 3 known ways that polyamines can enter the human body: food, synthesis by intestinal bacteria, and biosynthesis in the body. Currently, one of the most promising approaches to the prevention of cognitive impairment is the use of foods with a high content of polyamines, as well as the use of various probiotics that affect intestinal bacteria that synthesize polyamines. Since 2018, in a number of European countries projects have been launched aimed at evaluation of the impact of a diet high in polyamines on cognitive processes. The review, based on analysis of modern scientific literature and the authors' own data, presents material on the effect of polyamines on cognitive processes and the role of polyamines in the regulation of neurotransmitter processes, and discusses the role of polyamines in cognitive disorders in mental and neurological diseases.

Positive allosteric modulation of NMDA receptors: mechanisms, physiological impact and therapeutic potential

NMDA receptors (NMDARs) are glutamate-gated ion channels that play key roles in synaptic transmission and plasticity. Both hyper- and hypo-activation of NMDARs are deleterious to neuronal function. In particular, NMDAR hypofunction is involved in a wide range of neurological and psychiatric conditions like schizophrenia, intellectual disability, age-dependent cognitive decline, or Alzheimer's disease. While early medicinal chemistry efforts were mostly focused on the development of NMDAR antagonists, the last 10 years have seen a boom in the development of NMDAR positive allosteric modulators (PAMs). Here we review the currently developed NMDAR PAMs, their pharmacological profiles and mechanisms of action, as well as their physiological effects in healthy animals and animal models of NMDAR hypofunction. In light of the complexity of physiological outcomes of NMDAR PAMs in vivo, we discuss the remaining challenges and questions that need to be addressed to better grasp and predict the therapeutic potential of NMDAR positive allosteric modulation.

Alzheimer's disease as a chronic maladaptive polyamine stress response

Polyamines are nitrogen-rich polycationic ubiquitous bioactive molecules with diverse evolutionary-conserved functions. Their activity interferes with numerous genes' expression resulting in cell proliferation and signaling modulation. The intracellular levels of polyamines are precisely controlled by an evolutionary-conserved machinery. Their transient synthesis is induced by heat stress, radiation, and other traumatic stimuli in a process termed the polyamine stress response (PSR). Notably, polyamine levels decline gradually with age; and external supplementation improves lifespan in model organisms. This corresponds to cytoprotective and reactive oxygen species scavenging properties of polyamines. Paradoxically, age-associated neurodegenerative disorders are characterized by upsurge in polyamines levels, indicating polyamine pleiotropic, adaptive, and pathogenic roles. Specifically, arginase overactivation and arginine brain deprivation have been shown to play an important role in Alzheimer's disease (AD) pathogenesis. Here, we assert that a universal short-term PSR associated with acute stimuli is beneficial for survival. However, it becomes detrimental and maladaptive following chronic noxious stimuli, especially in an aging organism. Furthermore, we regard cellular senescence as an adaptive response to stress and suggest that PSR plays a central role in age-related neurodegenerative diseases' pathogenesis. Our perspective on AD proposes an inclusive reassessment of the causal relationships between the classical hallmarks and clinical manifestation. Consequently, we offer a novel treatment strategy predicated upon this view and suggest fine-tuning of arginase activity with natural inhibitors to preclude or halt the development of AD-related dementia.

Systemic and topical administration of spermidine accelerates skin wound healing

BACKGROUND

The skin wound healing process is regulated by various cytokines, chemokines, and growth factors. Recent reports have demonstrated that spermine/spermidine (SPD) promote wound healing through urokinase-type plasminogen activator (uPA)/uPA receptor (uPAR) signaling in vitro. Here, we investigated whether the systemic and topical administration of SPD would accelerate the skin wound-repair process in vivo.

METHODS

A skin wound repair model was established using C57BL/6 J mice. SPD was mixed with white petrolatum for topical administration. For systemic administration, SPD mixed with drinking water was orally administered. Changes in wound size over time were calculated using digital photography.

RESULTS

Systemic and topical SPD treatment significantly accelerated skin wound healing. The administration of SPD promoted the uPA/uPAR pathway in wound sites. Moreover, topical treatment with SPD enhanced the expression of IL-6 and TNF-α in wound sites. Scratch and cell proliferation assays revealed that SPD administration accelerated scratch wound closure and cell proliferation in vitro.

CONCLUSION

These results indicate that treatment with SPD promotes skin wound healing through activation of the uPA/uPAR pathway and induction of the inflammatory response in wound sites. The administration of SPD might contribute to new effective treatments to accelerate skin wound healing. Video Abstract.

Beyond Antioxidant Effects: Nature-Based Templates Unveil New Strategies for Neurodegenerative Diseases

The complex network of malfunctioning pathways occurring in the pathogenesis of neurodegenerative diseases (NDDs) represents a huge hurdle in the development of new effective drugs to be used in therapy. In this context, redox reactions act as crucial regulators in the maintenance of neuronal microenvironment homeostasis. Particularly, their imbalance results in the severe compromising of organism’s natural defense systems and subsequently, in the instauration of deleterious OS, that plays a fundamental role in the insurgence and progress of NDDs. Despite the huge efforts in drug discovery programs, the identification process of new therapeutic agents able to counteract the relentless progress of neurodegenerative processes has produced low or no effective therapies. Consequently, a paradigm-shift in the drug discovery approach for these diseases is gradually occurring, paving the way for innovative therapeutical approaches, such as polypharmacology. The aim of this review is to provide an overview of the main pharmacological features of most promising nature-based scaffolds for a possible application in drug discovery, especially for NDDs, highlighting their multifaceted effects against OS and neuronal disorders.

Aberrant AZIN2 and polyamine metabolism precipitates tau neuropathology

Tauopathies display a spectrum of phenotypes from cognitive to affective behavioral impairments; however, mechanisms promoting tau pathology and how tau elicits behavioral impairment remain unclear. We report a unique interaction between polyamine metabolism, behavioral impairment, and tau fate. Polyamines are ubiquitous aliphatic molecules that support neuronal function, axonal integrity, and cognitive processing. Transient increases in polyamine metabolism hallmark the cell's response to various insults, known as the polyamine stress response (PSR). Dysregulation of gene transcripts associated with polyamine metabolism in Alzheimer's disease (AD) brains were observed, and we found that ornithine decarboxylase antizyme inhibitor 2 (AZIN2) increased to the greatest extent. We showed that sustained AZIN2 overexpression elicited a maladaptive PSR in mice with underlying tauopathy (MAPT P301S; PS19). AZIN2 also increased acetylpolyamines, augmented tau deposition, and promoted cognitive and affective behavioral impairments. Higher-order polyamines displaced microtubule-associated tau to facilitate polymerization but also decreased tau seeding and oligomerization. Conversely, acetylpolyamines promoted tau seeding and oligomers. These data suggest that tauopathies launch an altered enzymatic signature that endorses a feed-forward cycle of disease progression. Taken together, the tau-induced PSR affects behavior and disease continuance, but may also position the polyamine pathway as a potential entry point for plausible targets and treatments of tauopathy, including AD.

Mechanisms by which autophagy regulates memory capacity in ageing

Autophagy agonists have been proposed to slow down neurodegeneration. Spermidine, a polyamine that acts as an autophagy agonist, is currently under clinical trial for the treatment of age‐related memory decline. How Spermidine and other autophagy agonists regulate memory and synaptic plasticity is under investigation. We set up a novel mouse model of mild cognitive impairment (MCI), in which middle‐aged (12‐month‐old) mice exhibit impaired memory capacity, lysosomes engulfed with amyloid fibrils (β‐amyloid and α‐synuclein) and impaired task‐induced GluA1 hippocampal post‐translation modifications. Subchronic treatment with Spermidine as well as the autophagy agonist TAT‐Beclin 1 rescued memory capacity and GluA1 post‐translational modifications by favouring the autophagy/lysosomal‐mediated degradation of amyloid fibrils. These findings provide new mechanistic evidence on the therapeutic relevance of autophagy enhancers which, by improving the degradation of misfolded proteins, slow down age‐related memory decline.

Spermidine-induced improvement of memory consolidation involves PI3K/Akt signaling pathway

Spermidine (SPD) is an endogenous polyamine that plays a facilitatory role in memory acquisition and consolidation. Memory consolidation occurs immediately after learning and again around 3-6 hours later. Current evidence indicates that the polyamine binding site at the NMDA receptor (NMDAr) mediates the effects of SPD on memory. While NMDAr activation increases brain-derived neurotrophic factor (BDNF) release, no study has investigated whether BDNF-activated signaling pathways, such as the phosphatidylinositol 3-kinase (PI3K)/Akt pathway play a role in SPD-induced improvement of memory consolidation. Therefore, the aim of the current study was to evaluate whether the TrkB receptor and the PI3K/Akt pathway are involved in the facilitatory effect of SPD on memory consolidation. Male Wistar rats were trained in the contextual conditioned fear task. SPD, ANA-12 (TrkB antagonist), and LY294002 (PI3K inhibitor) were administered immediately after training. The animals were tested 24 h after training. We found that SPD improved fear memory consolidation and that both ANA-12 and LY294002 prevented the facilitatory effect of SPD on memory. These results suggest that SPD-induced improvement of memory consolidation involves the activation of the TrkB receptor and PI3K/Akt pathway.

Spermidine/spermine-N1-acetyltransferase ablation impacts tauopathy-induced polyamine stress response

BACKGROUND

Tau stabilizes microtubules; however, in Alzheimer's disease (AD) and tauopathies, tau becomes hyperphosphorylated, aggregates, and results in neuronal death. Our group recently uncovered a unique interaction between polyamine metabolism and tau fate. Polyamines exert an array of physiological effects that support neuronal function and cognitive processing. Specific stimuli can elicit a polyamine stress response (PSR), resulting in altered central polyamine homeostasis. Evidence suggests that elevations in polyamines following a short-term stressor are beneficial; however, persistent stress and subsequent PSR activation may lead to maladaptive polyamine dysregulation, which is observed in AD, and may contribute to neuropathology and disease progression.

METHODS

Male and female mice harboring tau P301L mutation (rTg4510) were examined for a tau-induced central polyamine stress response (tau-PSR). The direct effect of tau-PSR byproducts on tau fibrillization and oligomerization were measured using a thioflavin T assay and a N2a split superfolder GFP-Tau (N2a-ssGT) cell line, respectively. To therapeutically target the tau-PSR, we bilaterally injected caspase 3-cleaved tau truncated at aspartate 421 (AAV9 Tau ΔD421) into the hippocampus and cortex of spermidine/spermine-N¹-acetyltransferase (SSAT), a key regulator of the tau-PSR, knock out (SSAT-/-), and wild type littermates, and the effects on tau neuropathology, polyamine dysregulation, and behavior were measured. Lastly, cellular models were employed to further examine how SSAT repression impacted tau biology.

RESULTS

Tau induced a unique tau-PSR signature in rTg4510 mice, notably in the accumulation of acetylated spermidine. In vitro, higher-order polyamines prevented tau fibrillization but acetylated spermidine failed to mimic this effect and even promoted fibrillization and oligomerization. AAV9 Tau ΔD421 also elicited a unique tau-PSR in vivo, and targeted disruption of SSAT prevented the accumulation of acetylated polyamines and impacted several tau phospho-epitopes. Interestingly, SSAT knockout mice presented with altered behavior in the rotarod task, the elevated plus maze, and marble burying task, thus highlighting the impact of polyamine homeostasis within the brain.

CONCLUSION

These data represent a novel paradigm linking tau pathology and polyamine dysfunction and that targeting specific arms within the polyamine pathway may serve as new targets to mitigate certain components of the tau phenotype.

Neural, Cellular and Molecular Mechanisms of Active Forgetting

The neurobiology of memory formation attracts much attention in the last five decades. Conversely, the rules that govern and the mechanisms underlying forgetting are less understood. In addition to retroactive interference, retrieval-induced forgetting and passive decay of time, it has been recently demonstrated that the nervous system has a diversity of active and inherent processes involved in forgetting. In Drosophila, some operate mainly at an early stage of memory formation and involves dopamine (DA) neurons, specific postsynaptic DA receptor subtypes, Rac1 activation and induces rapid active forgetting. In mammals, others regulate forgetting and persistence of seemingly consolidated memories and implicate the activity of DA receptor subtypes and AMPA receptors in the hippocampus (HP) and related structures to activate parallel signaling pathways controlling active time-dependent forgetting. Most of them may involve plastic changes in synaptic and extrasynaptic receptors including specific removal of GluA2 AMPA receptors. Forgetting at longer timescales might also include changes in adult neurogenesis in the dentate gyrus (DG) of the HP. Therefore, based on relevance or value considerations neuronal circuits may regulate in a time-dependent manner what is formed, stored, and maintained and what is forgotten.

Polyamines: Bio-Molecules with Diverse Functions in Plant and Human Health and Disease

Biogenic amines-polyamines (PAs), particularly putrescine, spermidine and spermine are ubiquitous in all living cells. Their indispensable roles in many biochemical and physiological processes are becoming commonly known, including promoters of plant life and differential roles in human health and disease. PAs positively impact cellular functions in plants-exemplified by increasing longevity, reviving physiological memory, enhancing carbon and nitrogen resource allocation/signaling, as well as in plant development and responses to extreme environments. Thus, one or more PAs are commonly found in genomic and metabolomics studies using plants, particulary during different abiotic stresses. In humans, a general decline in PA levels with aging occurs parallel with some human health disorders. Also, high PA dose is detrimental to patients suffering from cancer, aging, innate immunity and cognitive impairment during Alzheimer and Parkinson diseases. A dichotomy exists in that while PAs may increase longevity and reduce some age-associated cardiovascular diseases, in disease conditions involving higher cellular proliferation, their intake has negative consequences. Thus, it is essential that PA levels be rigorously quantified in edible plant sources as well as in dietary meats. Such a database can be a guide for medical experts in order to recommend which foods/meats a patient may consume and which ones to avoid. Accordingly, designing both high and low polyamine diets for human consumption are in vogue, particularly in medical conditions where PA intake may be detrimental, for instance, cancer patients. In this review, literature data has been collated for the levels of the three main PAs, putrescine, spermidine and spermine, in different edible sources-vegetables, fruits, cereals, nuts, meat, sea food, cheese, milk, and eggs. Based on our analysis of vast literature, the effects of PAs in human/animal health fall into two broad, Yang and Yin, categories: beneficial for the physiological processes in healthy cells and detrimental under pathological conditions.

Post-acquisition hippocampal blockade of the NMDA receptor subunit GluN2A but not GluN2B sustains spatial reference memory retention

While it has been shown that the blockade of N-methyl-d-aspartate type glutamate receptors (NMDARs) impairs memory acquisition, recent studies have reported that the post-acquisition administration of NMDAR antagonists suppresses spatial memory decay. These findings suggest that NMDARs are important not only for the acquisition of new memories but also for the decay of previously acquired memories. The present study investigated the contributions of specific NMDAR subunits to spatial memory decay using NVP-AAM077 (NVP), an NMDAR antagonist that preferentially binds to GluN2A subunits, and the selective GluN2B blocker Ro 25-6981 (Ro). Following Morris water maze training (four trials/day for four days), NVP and/or Ro were subchronically infused into the rat hippocampus for five days. Seven days after training, NVP-treated rats and NVP/Ro-treated rats explored the target area significantly more than the control and Ro-treated rats. These results demonstrate that post-acquisition treatment with NVP, but not Ro, suppresses the forgetting of previously acquired spatial memories. The NVP-treated rats more persistently explored the target area in the second test, which was conducted one day after the first, while the NVP/Ro-treated rats did not, which suggest that Ro treatment downregulates memory retention. In conclusion, the present results indicate that the NMDAR GluN2A and GluN2B subunits contribute to spatial memory deterioration and maintenance, respectively.

Modulation of learning and memory by natural polyamines

Spermine and spermidine are natural polyamines that are produced mainly via decarboxylation of l-ornithine and the sequential transfer of aminopropyl groups from S-adenosylmethionine to putrescine by spermidine synthase and spermine synthase. Spermine and spermidine interact with intracellular and extracellular acidic residues of different nature, including nucleic acids, phospholipids, acidic proteins, carboxyl- and sulfate-containing polysaccharides. Therefore, multiple actions have been suggested for these polycations, including modulation of the activity of ionic channels, protein synthesis, protein kinases, and cell proliferation/death, within others. In this review we summarize these neurochemical/neurophysiological/morphological findings, particularly those that have been implicated in the improving and deleterious effects of spermine and spermidine on learning and memory of naïve animals in shock-motivated and nonshock-motivated tasks, from a historical perspective. The interaction with the opioid system, the facilitation and disruption of morphine-induced reward and the effect of polyamines and putative polyamine antagonists on animal models of cognitive diseases, such as Alzheimer's, Huntington, acute neuroinflammation and brain trauma are also reviewed and discussed. The increased production of polyamines in Alzheimer's disease and the biphasic nature of the effects of polyamines on memory and on the NMDA receptor are also considered. In light of the current literature on polyamines, which include the description of an inborn error of the metabolism characterized by mild-to moderate mental retardation and polyamine metabolism alterations in suicide completers, we can anticipate that polyamine targets may be important for the development of novel strategies and approaches for understanding the etiopathogenesis of important central disorders and their pharmacological treatment.

A Nonrewarding NMDA Receptor Antagonist Impairs the Acquisition, Consolidation, and Expression of Morphine Conditioned Place Preference in Mice

N-methyl-D-aspartate (NMDA) receptor antagonists block morphine-induced conditioned place preference (CPP). Although polyamines are endogenous modulators of the NMDA receptor, it is not known whether polyaminergic agents induce CPP or modulate morphine-induced CPP. Here, we examined whether polyamine ligands modify morphine CPP acquisition, consolidation, and expression. Adult male albino Swiss mice received saline (0.9 % NaCl, intraperitoneally (i.p.)) or morphine (5 mg/kg, i.p.) and were respectively confined to a black or a white compartment for 30 min for four consecutive days for CPP induction. The effect of arcaine (3 mg/kg, i.p.) or spermidine (30 mg/kg, i.p.), respectively, an antagonist and an agonist of the polyamine-binding site at the NMDA receptor, on the acquisition, consolidation, and expression of morphine CPP was studied. In those experiments designed to investigate whether spermidine prevented or reversed the effect of arcaine, spermidine (30 mg/kg, i.p.) was administered 15 min before or 15 min after arcaine, respectively. Arcaine and spermidine did not induce CPP or aversion per se. Arcaine (3 mg/kg, i.p.) impaired the acquisition, consolidation, and expression of morphine CPP. Spermidine prevented the impairing effect of arcaine on the acquisition of morphine CPP but not the impairing effect of arcaine on consolidation or expression of morphine CPP. These results suggest that arcaine may impair morphine CPP acquisition by modulating the polyamine-binding site at the NMDA receptor. However, the arcaine-induced impairment of consolidation and expression of morphine CPP seems to involve other mechanisms.