Hormesis/preconditioning mechanisms, the nervous system and aging

Working with Convex Responses: Antifragility from Finance to Oncology

We extend techniques and learnings about the stochastic properties of nonlinear responses from finance to medicine, particularly oncology, where it can inform dosing and intervention. We define antifragility. We propose uses of risk analysis for medical problems, through the properties of nonlinear responses (convex or concave). We (1) link the convexity/concavity of the dose-response function to the statistical properties of the results; (2) define "antifragility" as a mathematical property for local beneficial convex responses and the generalization of "fragility" as its opposite, locally concave in the tails of the statistical distribution; (3) propose mathematically tractable relations between dosage, severity of conditions, and iatrogenics. In short, we propose a framework to integrate the necessary consequences of nonlinearities in evidence-based oncology and more general clinical risk management.

The Hormesis Model for Building Resilience Through Adversity: Attention to Mechanism in Developmental Context

In developmental science, resilience refers to children and youths’ ability to recover and pursue positive development in the face of stress related to adversity. Extant research has documented protective factors and ecological contexts that mitigate the impact of adversity and thereby promote resilience. One intriguing aspect of resilience is that individuals also develop strength in response to early adversity. However, very little theoretical guidance exists on the developmental mechanisms and contexts through which early adversity may lead to strengthening effects that confer the process of resilience. The strengthening mechanism in the context of specific circumscribed environmental stress is a process known in the field of toxicology as hormesis. It is proposed here that the study of resilience in developmental and psychological sciences can benefit from shifting more attention to the hormesis model. The hormesis model is reviewed and discussed as a promising perspective on mechanisms, developmental timing, and context through which adversity strengthens or impedes resilience.

Neurohormetic phytochemicals in the pathogenesis of neurodegenerative diseases

The world population is progressively ageing, assuming an enormous social and health challenge. As the world ages, neurodegenerative diseases are on the rise. Regarding the progressive nature of these diseases, none of the neurodegenerative diseases are curable at date, and the existing treatments can only help relieve the symptoms or slow the progression. Recently, hormesis has increased attention in the treatment of age-related neurodegenerative diseases. The concept of hormesis refers to a biphasic dose-response phenomenon, where low levels of the drug or stress exert protective of beneficial effects and high doses deleterious or toxic effects. Neurohormesis, as the adaptive aspect of hormetic dose responses in neurons, has been shown to slow the onset of neurodegenerative diseases and reduce the damages caused by aging, stroke, and traumatic brain injury. Hormesis was also observed to modulate anxiety, stress, pain, and the severity of seizure. Thus, neurohormesis can be considered as a potentially innovative approach in the treatment of neurodegenerative and other neurologic disorders. Herbal medicinal products and supplements are often considered health resources with many applications. The hormesis phenomenon in medicinal plants is valuable and several studies have shown that hormetic mechanisms of bioactive compounds can prevent or ameliorate the neurodegenerative pathogenesis in animal models of Alzheimer’s and Parkinson’s diseases. Moreover, the hormesis activity of phytochemicals has been evaluated in other neurological disorders such as Autism and Huntington’s disease. In this review, the neurohormetic dose–response concept and the possible underlying neuroprotection mechanisms are discussed. Different neurohormetic phytochemicals used for the better management of neurodegenerative diseases, the rationale for using them, and the key findings of their studies are also reviewed.

Hormetic dose-response of halogenated organic pollutants on Microcystis aeruginosa: Joint toxic action and mechanism

Quinolones (QNs), dechloranes (DECs), and chlorinated paraffins (CPs) are three kinds of new halogenated organic pollutants (HOPs), which originate from the use of flame retardants, lubricants and pesticides. Since QNs, DECs, and CPs are frequently detected in waters and sediments, it is necessary to investigate the toxic effects of these HOPs with dwelling phytoplankton, especially for cyanobacteria, to explore their potential hormetic effects and contributions to algal blooms. In the present study, we investigate single and joint toxicity of QNs, DECs and CPs on Microcystis aeruginosa (M. aeruginosa), a cyanobacterium that is frequently implicated with algal blooms. The results indicate single QNs and DECs induce marked hormetic effects on the proliferation of M. aeruginosa but CPs do not. The stimulatory effect of hormesis is linked with accelerated replication of DNA, which is considered to stem from the moderate rise in intracellular reactive oxygen species (ROS). Joint toxicity tests reveal that both QNs & CPs mixtures and DECs & CPs mixtures show hormetic effects on M. aeruginosa, but QNs & DECs mixtures show no hormetic effect. QNs & DECs mixtures exhibit synergistic toxic actions, which may be caused by a sharp rise in intracellular ROS simultaneously produced by the agents. Joint toxic actions of both QNs & CPs, and DECs & CPs shift from addition to antagonism as concentration increases, and this shift may mainly depend on the influence of CPs on cell membrane hydrophobicity of M. aeruginosa. This study provides data and toxic mechanisms for the hormetic phenomenon of single and joint HOPs on M. aeruginosa. The hormetic effects of HOPs may benefit the proliferation of M. aeruginosa in the aquatic environment, aggravating the formation of algal blooms. This study also reflects the important role of hormesis in environmental risk assessment of pollutants.

Involvement of O2·- release in zearalenone-induced hormesis of intestinal porcine enterocytes: An electrochemical sensor-based analysis

Relationship between mycotoxin-induced hormesis and reactive oxygen species (ROS) has not been systematically investigated due to the lack of an effective analysis method. To monitor cellular release and intracellular level of O2·-, carboxymethyl cellulose-Mn3(PO4)2 nanocomposite was synthesized to fabricate an electrochemical biosensor, which selectively detects O2·- over the range of 57.50 nM ∼ 2.95 μM (R2 = 0.99) with the sensitivity of 78.67 μA μM-1 cm-2 and the detection limit of 8.47 nM. Transient exposure to zearalenone (ZEA) induces the enhancement on cell viability, immediate O2·- release from cells, and reduction of intracellular O2·- level. After post-treatment culture, intracellular O2·- initially increases to a high level and then decreases to the normal level. Concurrently, the ZEA-induced hormesis disappears. Based on the findings, we propose a mechanism, involving the ROS release, increase of succinate dehydrogenase activity and recovery of intracellular ROS, to explain the occurrence and disappearance of hormesis in intestinal porcine enterocytes.

Habitual- and Meal-Specific Carbohydrate Quality Index and Their Relation to Metabolic Syndrome in a Sample of Iranian Adults

Aim

Most studies on diet quality have focused on the habitual and overall intake of foods without considering intakes at specific eating occasions. This study aimed to assess the association between habitual- and meal-specific carbohydrate quality index (CQI) and metabolic syndrome (MetS) in Iranian adults.

Methods

In this cross-sectional study, data from 850 participants were analyzed. Dietary information was obtained from a 3-day nonconsecutive 24 h recall. CQI was calculated from three criteria: dietary fiber, glycemic index, and solid carbohydrate/total carbohydrate ratio. The association between CQI and MetS was assessed by logistic regression.

Results

The prevalences of MetS in the lowest and highest tertile of CQI were 30.1 and 33.7, respectively (P = 0.6). In habitual diet and all the three meals, we failed to find any significant association between tertiles of CQI and MetS either before or after adjustment for covariates. However, in the habitual meals [odds ratio (OR): 0.69, 95% CI: 0.47–0.96] and lunch meals (OR: 0.66; 95% CI: 0.47–0.94), the highest CQI in comparison to the lowest one, significantly decreased the low high-density lipoprotein (HDL). In addition, the trend of low-HDL with CQI in habitual meal and lunch meal was statistically significant.

Conclusion

The results of this study showed that CQI was not associated with MetS and its components. Further investigations into the mechanisms underlying the role of carbohydrate quality in developing metabolic disorders are warranted.

Therapeutic Potential of Mitophagy-Inducing Microflora Metabolite, Urolithin A for Alzheimer's Disease

Mitochondrial dysfunction including deficits of mitophagy is seen in aging and neurodegenerative disorders including Alzheimer’s disease (AD). Apart from traditionally targeting amyloid beta (Aβ), the main culprit in AD brains, other approaches include investigating impaired mitochondrial pathways for potential therapeutic benefits against AD. Thus, a future therapy for AD may focus on novel candidates that enhance optimal mitochondrial integrity and turnover. Bioactive food components, known as nutraceuticals, may serve as such agents to combat AD. Urolithin A is an intestinal microbe-derived metabolite of a class of polyphenols, ellagitannins (ETs). Urolithin A is known to exert many health benefits. Its antioxidant, anti-inflammatory, anti-atherogenic, anti-Aβ, and pro-mitophagy properties are increasingly recognized. However, the underlying mechanisms of urolithin A in inducing mitophagy is poorly understood. This review discusses the mitophagy deficits in AD and examines potential molecular mechanisms of its activation. Moreover, the current knowledge of urolithin A is discussed, focusing on its neuroprotective properties and its potential to induce mitophagy. Specifically, this review proposes potential mechanisms by which urolithin A may activate and promote mitophagy.

The possible hormetic effects of fluorene-9-bisphenol on regulating hypothalamic-pituitary-thyroid axis in zebrafish

Fluorene-9-bisphenol (BHPF) is a bisphenol A substitute, which has been introduced for the production of so-called 'bisphenol A (BPA)-free' plastics. However, it has been reported that BHPF can enter living organisms through using commercial plastic bottles and cause adverse effects. To date, the majority of the toxicologic study of BHPF focused on investigating its doses above the toxicological threshold. Here, we studied the effects of BHPF on development, locomotion, neuron differentiation of the central nervous system (CNS), and the expression of genes in the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish exposed to different doses of BHPF ranging from 1/5 of LD1 to LD50 (300, 500, 750, 1500, 3000, and 4500 nM). As a result, the possible hormetic effects of BHPF on regulating the HPT axis were revealed, in which low-dose BHPF positively affected the HPT axis while this regulation was inhibited as the dose increased. Underlying mechanism investigation suggested that BHPF disrupted myelination through affecting HPT axis including related genes expression and TH levels, thus causing neurotoxic characteristics. Collectively, this study provides the full understanding of the environmental impact of BHPF and its toxicity on living organisms, highlighting a substantial and generalized ongoing dose-response relationship with great implications for the usage and risk assessment of BHPF.

The Muscle-Brain Axis and Neurodegenerative Diseases: The Key Role of Mitochondria in Exercise-Induced Neuroprotection

Regular exercise is associated with pronounced health benefits. The molecular processes involved in physiological adaptations to exercise are best understood in skeletal muscle. Enhanced mitochondrial functions in muscle are central to exercise-induced adaptations. However, regular exercise also benefits the brain and is a major protective factor against neurodegenerative diseases, such as the most common age-related form of dementia, Alzheimer's disease, or the most common neurodegenerative motor disorder, Parkinson's disease. While there is evidence that exercise induces signalling from skeletal muscle to the brain, the mechanistic understanding of the crosstalk along the muscle-brain axis is incompletely understood. Mitochondria in both organs, however, seem to be central players. Here, we provide an overview on the central role of mitochondria in exercise-induced communication routes from muscle to the brain. These routes include circulating factors, such as myokines, the release of which often depends on mitochondria, and possibly direct mitochondrial transfer. On this basis, we examine the reported effects of different modes of exercise on mitochondrial features and highlight their expected benefits with regard to neurodegeneration prevention or mitigation. In addition, knowledge gaps in our current understanding related to the muscle-brain axis in neurodegenerative diseases are outlined.

Neuroprotective effects of natural compounds on neurotoxin-induced oxidative stress and cell apoptosis

OBJECTIVES

Overproduction of reactive species, notably reactive oxygen (ROS) and nitrogen (RNS) species, along with the failure of balancing effects of endogenous antioxidant defenses result in destruction of cellular structures, lipids, proteins, and genetic material, which lead to oxidative stress. Oxidative stress-induced neuronal apoptosis plays a pivotal role in pathogenesis of neurodegeneration. Antioxidants represent one of the medical choice strategies for protecting against this unbalanced oxidation-antioxidation status. Recently, natural compounds with neuroprotective potential that can scavenge free radicals and protect cells from oxidative damage have received extensive attention.

METHODS

In this review, we summarized the detailed research progress on the medicinal plants-derived natural compounds with potential anti-oxidation effects and their molecular mechanisms on modulating the neurotoxin (6-OHDA, H₂O₂, glutamate, Aβ)-induced oxidative stress and cell apoptosis.

RESULTS

The natural compounds that efficacious in modulating reactive species production and mitochondrial function include flavonoids, glucosides, alkaloids, polyphenols, lignans, coumarins, terpenoids, quinones and others. They decreased the neurotoxin-induced oxidative damage and apoptosis by (1) decreasing ROS/RNS generation, lipid peroxidation, caspase-3 and caspase-9 activities, LDH release, the ratio of Bax/Bcl-2, Ca²⁺ influx and cytochrome c release, (2) elevating MMP, and (3) restoring endogenous antioxidant enzymatic activities (CAT, GSH-Px, GSR, SOD). And they exerted neuroprotective effects against cell damages and apoptosis by modulating the oxidative cascades of different signaling pathways (Nrf2/HO-1, NF-κB, MAPKs, PI3K/Akt, GSK-3β) and preventing mitochondria-dependent apoptosis pathways.

DISCUSSION

The present work reviews the role of oxidative stress in neurodegeneration, highlighting the potential anti-oxidation effects of natural compounds as a promising approach to develop innovative neuroprotective strategy.

Potential of Caenorhabditis elegans as an antiaging evaluation model for dietary phytochemicals: A review

Aging is an inevitable process characterized by the accumulation of degenerative damage, leading to serious diseases that affect human health. Studies on aging aim to develop pre-protection or therapies to delay aging and age-related diseases. A preventive approach is preferable to clinical treatment not only to reduce investment but also to alleviate pain in patients. Adjusting daily diet habits to improve the aging condition is a potentially attractive strategy. Fruits and vegetables containing active compounds that can effectively delay the aging process and reduce or inhibit age-related degenerative diseases have been identified. The signaling pathways related to aging in Caenorhabditis elegans are evolutionarily conserved; thus, studying antiaging components by intervening senescence process may contribute to the prevention and treatment of age-related diseases in humans. This review focuses on the effects of food-derived extracts or purified substance on antiaging in nematodes, as well as the underlying mechanisms, on the basis of several major signaling pathways and key regulatory factors in aging. The aim is to provide references for a healthy diet guidance and the development of antiaging nutritional supplements. Finally, challenges in the use of C. elegans as the antiaging evaluation model are discussed, together with the development that potentially inspire novel strategies and research tools.

Hormesis: A potential strategic approach to the treatment of neurodegenerative disease

This review describes neuroprotective effects mediated by pre- and post-conditioning-induced processes that act via the quantitative features of the hormetic dose response. These lead to the development of acquired resilience that can protect neuronal systems from endogenous and exogenous stresses and insult. Particular attention is directed to issues of dose optimization, inter-individual variation, and potential ways to further study and employ hormetic-based preconditioning approaches in medical and public health efforts to treat and prevent neurodegenerative disease.

A trigger mechanism of herbicides to phytoplankton blooms: From the standpoint of hormesis involving cytochrome b559, reactive oxygen species and nitric oxide

The cause of phytoplankton blooms has been extensively discussed and largely attributed to favorable external conditions such as nitrogen/phosphorus resources, pH and temperature. Here from the standpoint of hormesis response, we propose that phytoplankton blooms are initiated by stimulatory effects of low concentrations of herbicides as environmental contaminants spread over estuaries and lakes. The experimental results revealed general stimulations by herbicides on Microcystis aeruginosa and Selenastrum capricornutum, with the maximum stimulation in the 30-60% range, depending on the agent and experiment. In parallel with enhancing stimulation, the ratio of HP (high-potential) form to LP (low-potential) form of cytochrome b₅₅₉ (RHL) was observed decreasing, while intracellular reactive oxygen species (ROS) were observed increasing. We propose that the ROS originated from the thermodynamic transformation of cytochrome b₅₅₉, enhancing the stimulatory response. Furthermore, the results also proved that thermodynamic states of cytochrome b₅₅₉ could be modulated by nitric oxide, thus affecting cellular equilibrium of oxidative stress (OS) and correspondingly causing the inhibitory effect of higher concentrations of herbicides on phytoplankton. This suggests that hormesis substantially derives from equilibrium shifting of OS. Moreover, it is reasonable to infer that phytoplankton blooms would be motivated by herbicides or other environmental pollutants. This study provides a new thought into global phytoplankton blooms from a contaminant perspective.

A brief physical activity protects against ischemic stroke

With restricted therapeutic opportunities, stroke remains a relevant, critical disease necessitating study. Due to the unique aspect of ischemic strokes, finding approaches to maintain the vigor of the cerebral vasculature, such as increased angiogenesis, may protect against stroke. Ischemic strokes are caused by disruptions in blood movement in the brain, resulting in a torrent of harmful cerebrovasculature modifications. In an investigation by Pianta et al., Sprague-Dawley rats have been separated into those that undergo exercise prior to middle cerebral artery occlusion (MCAO) and those that were not exposed to physical activity preceding MCAO. The outcomes and results of the current study gave new insights into the capacity of exercise to help prevent ischemic strokes or mitigate poststroke effects. The data collected from the study suggested that rats that went through a short bout of exercise before MCAO presented superior motor performance, more active cells in the peri-infarct region, and reduced infarct sizes. When compared to the control group, the rats that went through exercise also had heightened angiogenesis and improved neuroprotection. Thus, a brief bout of physical activity preceding a stroke may provide neuroprotection by enhancing the strength of the cerebrovasculature in the brain. This notion that even an instant of physical exercise before a stroke is induced can help dampen the effects of ischemic stroke, which could lead to future techniques in preventing the ischemic stroke so that it never happens at all.

Impacts of in vivo and in vitro exposures to tamoxifen: Comparative effects on human cells and marine organisms

Tamoxifen (TAM) is a first generation-SERM administered for hormone receptor-positive (HER+) breast cancer in both pre- and post-menopausal patients and may undergo metabolic activation in organisms that share similar receptors and thus face comparable mechanisms of response. The present study aimed to assess whether environmental trace concentrations of TAM are bioavailable to the filter feeder M. galloprovincialis (100 ng L^-1) and to the deposit feeder N. diversicolor (0.5, 10, 25 and 100 ng L^-1) after 14 days of exposure. Behavioural impairment (burrowing kinetic), neurotoxicity (AChE activity), endocrine disruption by alkali-labile phosphate (ALP) content, oxidative stress (SOD, CAT, GPXs activities), biotransformation (GST activity), oxidative damage (LPO) and genotoxicity (DNA damage) were assessed. Moreover, this study also pertained to compare TAM cytotoxicity effects to mussels and targeted human (i.e. immortalized retinal pigment epithelium - RPE; and human transformed endothelial cells - HeLa) cell lines, in a range of concentrations from 0.5 ng L^-1 to 50 μg L^-1. In polychaetes N. diversicolor, TAM exerted remarkable oxidative stress and damage at the lowest concentration (0.5 ng L^-1), whereas significant genotoxicity was reported at the highest exposure level (100 ng L^-1). In mussels M. galloprovincialis, 100 ng L^-1 TAM caused endocrine disruption in males, neurotoxicity, and an induction in GST activity and LPO byproducts in gills, corroborating in genotoxicity over the exposure days. Although cytotoxicity assays conducted with mussel haemocytes following in vivo exposure was not effective, in vitro exposure showed to be a feasible alternative, with comparable sensitivity to human cell line (HeLa).

Panax notoginseng saponins promote liver regeneration through activation of the PI3K/AKT/mTOR cell proliferation pathway and upregulation of the AKT/Bad cell survival pathway in mice

Backgroud

The regenerative capacity of the liver is crucial for the host to survive after serious hepatic injuries, tumor resection, or living donor liver transplantation. Panax notoginseng saponins (PNS) have been reported to exert protective effects during organ injuries. The present study aimed to evaluate the effect of PNS on liver regeneration(LR) and on injuries induced by partial hepatectomy (PH).

Methods

We performed 70% partial PH on C57BL/6 J mice treated with or without PNS. LR was estimated by liver weight/body weight, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and cell proliferation, and the related cellular signals were analyzed by Western blot.

Results

Different concentrations of PNS promoted hepatocyte proliferation in vitro. Mice in the PNS group showed higher liver/body weight ratios at 2 d and 7 d (P < 0.05) after PH and lower levels of serum ALT and AST (P < 0.05) compared to those of mice in the normal control (NC) group. Histological analysis showed that the expression of proliferating cell nuclear antigen(PCNA) at 2 d and 7 d after PH was significantly higher in the PNS group than in the NC group (P < 0.05). Mechanistically, the AKT/mTOR cell proliferation pathway and AKT/Bad cell survival pathway were activated by PNS, which accelerated hepatocyte proliferation and inhibited apoptosis (P < 0.05).

Conclusions

PNS promoted liver regeneration through activation of PI3K/AKT/mTOR and upregulated the AKT/Bad cell pathways in mice.

A Short Bout of Exercise Prior to Stroke Improves Functional Outcomes by Enhancing Angiogenesis

Stroke remains a significant unmet clinical need with limited therapeutic options. The peculiar feature of ischemic stroke is the interruption in brain circulation, resulting in a cascade of detrimental cerebrovasculature alterations. Treatment strategies designed to maintain potency of the cerebrovasculature may protect against stroke. The present study assessed the effects of short bouts of exercise prior to stroke induction and characterized cerebral blood flow and motor functions in vivo. Adult Sprague-Dawley rats were exposed to a single short bout of exercise (30-min or 60-min forced running wheel) then subjected to transient middle cerebral artery occlusion (MCAO). Non-exercise stroke rats served as controls while non-stroke rats represented shams. Cerebral blood flow (CBF) was evaluated by laser Doppler at baseline (prior to MCAO), during MCAO, and during reperfusion. Behavioral tests using the elevated body swing test was conducted at baseline, day 0 (day of stroke), and at days 1 and 3 after stroke. Animals that received exercise displayed typical alterations in CBF after stroke, but exhibited improved motor performance compared to non-exercise rats. Exercised stroke rats showed a reduction in infarct size and an increased number of surviving cells in the peri-infarct area, with a trend towards prolonged duration of the exercise. Immunofluorescence staining and Western blot analysis of the peri-infarct area revealed increased levels of endothelial markers/angiogenesis markers, VEGF, VEGFR-2, and Ang-2, and endothelial progenitor cell marker CD34+ in exercise groups compared with the controls. These results demonstrated that prophylactic exercise affords neuroprotection possibly by improving cerebrovascular potency.

Hormetic effects of curcumin: What is the evidence?

Curcumin (diferuloylmethane), a component of the yellow powder prepared from the roots of Curcuma longa or Zingiberaceae (known as turmeric) is not only widely used to color and flavor food but also used as a pharmaceutical agent. Curcumin demonstrates anti-inflammatory, anticarcinogenic, antiaging, and antioxidant activity, as well as efficacy in wound healing. Notably, curcumin is a hormetic agent (hormetin), as it is stimulatory at low doses and inhibitory at high doses. Hormesis by curcumin could be also a particular function at low doses (i.e., antioxidant behavior) and another function at high dose (i.e., induction of autophagy and cell death). Recent findings suggest that curcumin exhibits biphasic dose-responses on cells, with low doses having stronger effects than high doses; examples being activation of the mitogen-activated protein kinase signaling pathway or antioxidant activity. This indicates that many effects induced by curcumin are dependent on dose and some effects might be greater at lower doses, indicative of a hormetic response. Despite the consistent occurrence of hormetic responses of curcumin in a wide range of biomedical models, epidemiological and clinical trials are needed to assess the nature of curcumin's dose-response in humans. Fortunately, more than one hundred clinical trials with curcumin and curcumin derivatives are ongoing. In this review, we provide the first comprehensive analysis supportive of the hormetic behavior of curcumin and curcumin derivatives.

Neuron-specific overexpression of core clock genes improves stress-resistance and extends lifespan of Drosophila melanogaster

Gene expression is much altered in aging. We observed age-dependent decline of core clock genes' expression in the whole body of the fruit fly. We hypothesized that inducible overexpression of clock genes (cry, per, tim, cyc and Clk) in the nervous system can improve healthspan of D. melanogaster. We studied the lifespan of transgenic Drosophila and showed life extension for cry, per, cyc and tim genes. It was also the significant positive changes in the stress-resistance of flies overexpressing core clock genes in conditions of hyperthermia, hyperoxia, starvation and persistent lighting. The overexpression of per and cry restore circadian rhythms of locomotor activity. The results presented support the hypotheses that the compensation of circadian oscillator genes expression can improve the healthspan in Drosophila melanogaster.

How does hormesis impact biology, toxicology, and medicine?

Hormesis refers to adaptive responses of biological systems to moderate environmental or self-imposed challenges through which the system improves its functionality and/or tolerance to more severe challenges. The past two decades have witnessed an expanding recognition of the concept of hormesis, elucidation of its evolutionary foundations, and underlying cellular and molecular mechanisms, and practical applications to improve quality of life. To better inform future basic and applied research, we organized and re-evaluated recent hormesis-related findings with the intent of incorporating new knowledge of biological mechanisms, and providing fundamental insights into the biological, biomedical and risk assessment implications of hormesis. As the literature on hormesis is expanding rapidly into new areas of basic and applied research, it is important to provide refined conceptualization of hormesis to aid in designing and interpreting future studies. Here, we establish a working compartmentalization of hormesis into ten categories that provide an integrated understanding of the biological meaning and applications of hormesis.

Berberine protects against 6-OHDA-induced neurotoxicity in PC12 cells and zebrafish through hormetic mechanisms involving PI3K/AKT/Bcl-2 and Nrf2/HO-1 pathways

Berberine (BBR) is a renowned natural compound that exhibits potent neuroprotective activities. However, the cellular and molecular mechanisms are still unclear. Hormesis is an adaptive mechanism generally activated by mild oxidative stress to protect the cells from further damage. Many phytochemicals have been shown to induce hormesis. This study aims to investigate whether the neuroprotective activity of BBR is mediated by hormesis and the related signaling pathways in 6-OHDA-induced PC12 cells and zebrafish neurotoxic models. Our results demonstrated that BBR induced a typical hormetic response in PC12 cells, i.e. low dose BBR significantly increased the cell viability, while high dose BBR inhibited the cell viability. Moreover, low dose BBR protected the PC12 cells from 6-OHDA-induced cytotoxicity and apoptosis, whereas relatively high dose BBR did not show neuroprotective activity. The hormetic and neuroprotective effects of BBR were confirmed to be mediated by up-regulated PI3K/AKT/Bcl-2 cell survival and Nrf2/HO-1 antioxidative signaling pathways. In addition, low dose BBR markedly mitigated the 6-OHDA-induced dopaminergic neuron loss and behavior movement deficiency in zebrafish, while high dose BBR only slightly exhibited neuroprotective activities. These results strongly suggested that the neuroprotection of BBR were attributable to the hormetic mechanisms via activating cell survival and antioxidative signaling pathways.

Exercise, oxidants, and antioxidants change the shape of the bell-shaped hormesis curve

It is debated whether exercise-induced ROS production is obligatory to cause adaptive response. It is also claimed that antioxidant treatment could eliminate the adaptive response, which appears to be systemic and reportedly reduces the incidence of a wide range of diseases. Here we suggest that if the antioxidant treatment occurs before the physiological function-ROS dose-response curve reaches peak level, the antioxidants can attenuate function. On the other hand, if the antioxidant treatment takes place after the summit of the bell-shaped dose response curve, antioxidant treatment would have beneficial effects on function. We suggest that the effects of antioxidant treatment are dependent on the intensity of exercise, since the adaptive response, which is multi pathway dependent, is strongly influenced by exercise intensity. It is further suggested that levels of ROS concentration are associated with peak physiological function and can be extended by physical fitness level and this could be the basis for exercise pre-conditioning. Physical inactivity, aging or pathological disorders increase the sensitivity to oxidative stress by altering the bell-shaped dose response curve.

Hormetic effect of panaxatriol saponins confers neuroprotection in PC12 cells and zebrafish through PI3K/AKT/mTOR and AMPK/SIRT1/FOXO3 pathways

Hormesis is an adaptive response of living organisms to a moderate stress. However, its biomedical implication and molecular mechanisms remain to be intensively investigated. Panaxatriol saponins (PTS) is the major bioactive components extracted from Panax notoginseng, a widely used herbal medicine for cerebrovascular diseases. This study aims to examine the hormetic and neuroprotective effects of PTS in PC12 cells and zebrafish Parkinson's disease (PD) models. Our results demonstrated that PTS stimulated PC12 cell growth by about 30% at low doses, while PTS at high doses inhibited cell growth, which is a typical hormetic effect. Moreover, we found that low dose PTS pretreatment significantly attenuated 6-OHDA-induced cytotoxicity and up-regulated PI3K/AKT/mTOR cell proliferation pathway and AMPK/SIRT1/FOXO3 cell survival pathway in PC12 cells. These results strongly suggested that neuroprotective effects of PTS may be attributable to the hormetic effect induced by PTS through activating adaptive response-related signaling pathways. Notably, low dose PTS could significantly prevent the 6-OHDA-induced dopaminergic neuron loss and improve the behavior movement deficiency in zebrafish, whereas relative high dose PTS exhibited neural toxicity, further supporting the hormetic and neuroprotective effects of PTS. This study indicates that PTS may have the potential in the development of future therapeutic medicines for PD.

Phytochemicals in Ischemic Stroke

Stroke is the second foremost cause of mortality worldwide and a major cause of long-term disability. Due to changes in lifestyle and an aging population, the incidence of stroke continues to increase and stroke mortality predicted to exceed 12 % by the year 2030. However, the development of pharmacological treatments for stroke has failed to progress much in over 20 years since the introduction of the thrombolytic drug, recombinant tissue plasminogen activator. These alarming circumstances caused many research groups to search for alternative treatments in the form of neuroprotectants. Here, we consider the potential use of phytochemicals in the treatment of stroke. Their historical use in traditional medicine and their excellent safety profile make phytochemicals attractive for the development of therapeutics in human diseases. Emerging findings suggest that some phytochemicals have the ability to target multiple pathophysiological processes involved in stroke including oxidative stress, inflammation and apoptotic cell death. Furthermore, epidemiological studies suggest that the consumption of plant sources rich in phytochemicals may reduce stroke risk, and so reinforce the possibility of developing preventative or neuroprotectant therapies for stroke. In this review, we describe results of preclinical studies that demonstrate beneficial effects of phytochemicals in experimental models relevant to stroke pathogenesis, and we consider their possible mechanisms of action.

Linking Mitochondria to Synapses: New Insights for Stress-Related Neuropsychiatric Disorders

The brain evolved cellular mechanisms for adapting synaptic function to energy supply. This is particularly evident when homeostasis is challenged by stress. Signaling loops between the mitochondria and synapses scale neuronal connectivity with bioenergetics capacity. A biphasic “inverted U shape” response to the stress hormone glucocorticoids is demonstrated in mitochondria and at synapses, modulating neural plasticity and physiological responses. Low dose enhances neurotransmission, synaptic growth, mitochondrial functions, learning, and memory whereas chronic, higher doses produce inhibition of these functions. The range of physiological effects by stress and glucocorticoid depends on the dose, duration, and context at exposure. These criteria are met by neuronal activity and the circadian, stress-sensitive and ultradian, stress-insensitive modes of glucocorticoid secretion. A major hallmark of stress-related neuropsychiatric disorders is the disrupted glucocorticoid rhythms and tissue resistance to signaling with the glucocorticoid receptor (GR). GR resistance could result from the loss of context-dependent glucocorticoid signaling mediated by the downregulation of the activity-dependent neurotrophin BDNF. The coincidence of BDNF and GR signaling changes glucocorticoid signaling output with consequences on mitochondrial respiration efficiency, synaptic plasticity, and adaptive trajectories.

HORMESIS: A Fundamental Concept with Widespread Biological and Biomedical Applications

Hormesis is a biphasic dose response with specific quantitative features for the amplitude and width of the stimulation. It is highly generalizable and independent of biological model, endpoint, inducing agent, level of biological organization and mechanism. Hormesis may be induced via a direct stimulation or by overcompensation to a disruption of homeostasis. The induction of hormesis by low-level stressor agents not only rapidly upregulates adaptive processes to repair damage but also protects the adapted system from damage due to a subsequent challenging dose (toxic) within a definable temporal window. The striking consistency of the amplitude of hormetic response suggests that hormesis provides a quantitative description of biological plasticity. Knowledge of hormesis has particular potential biomedical significance with respect to slowing or retarding both normal aging processes and the progression of severe neurological diseases.

Heat shock proteins and hormesis in the diagnosis and treatment of neurodegenerative diseases

Modulation of endogenous cellular defense mechanisms via the vitagene system represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. The possibility of high-throughoutput screening using proteomic techniques, particularly redox proteomics, provide more comprehensive overview of the interaction of proteins, as well as the interplay among processes involved in neuroprotection. Here by introducing the hormetic dose response concept, the mechanistic foundations and applications to the field of neuroprotection, we discuss the emerging role of heat shock protein as prominent member of vitagene network in neuroprotection and redox proteomics as a tool for investigating redox modulation of stress responsive vitagenes. Hormetic mechanisms are reviewed as possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the neurodegenerative disease process.

Effect of temperature on replicative aging of the budding yeast Saccharomyces cerevisiae

The use of the budding yeast Saccharomyces cerevisiae in gerontological studies was based on the assumption that the reproduction limit of a single cell (replicative aging) is a consequence of accumulation of a hypothetical universal "senescence factor" within the mother cell. However, some evidence suggests that molecules or structures proposed as the "aging factor", such as rDNA circles, oxidatively damaged proteins (with carbonyl groups) or mitochondria, have little effect on replicative lifespan of yeast cells. Our results also suggest that protein aggregates associated with Hsp104, treated as a marker of yeast aging, do not seem to affect the numeric value of replicative lifespan of yeast. What these results indicate, however, is the need for finding a different way of expressing age and longevity of yeast cells instead of the commonly used number of daughters produced over units of time, as in the case of other organisms. In this paper, we show that the temperature has a stronger influence on the time of life (the total lifespan) than on the reproductive potential of yeast cells.

Physical exercise in overweight to obese individuals induces metabolic- and neurotrophic-related structural brain plasticity

Previous cross-sectional studies on body-weight-related alterations in brain structure revealed profound changes in the gray matter (GM) and white matter (WM) that resemble findings obtained from individuals with advancing age. This suggests that obesity may lead to structural brain changes that are comparable with brain aging. Here, we asked whether weight-loss-dependent improved metabolic and neurotrophic functioning parallels the reversal of obesity-related alterations in brain structure. To this end we applied magnetic resonance imaging (MRI) together with voxel-based morphometry and diffusion-tensor imaging in overweight to obese individuals who participated in a fitness course with intensive physical training twice a week over a period of 3 months. After the fitness course, participants presented, with inter-individual heterogeneity, a reduced body mass index (BMI), reduced serum leptin concentrations, elevated high-density lipoprotein-cholesterol (HDL-C), and alterations of serum brain-derived neurotrophic factor (BDNF) concentrations suggesting changes of metabolic and neurotrophic function. Exercise-dependent changes in BMI and serum concentration of BDNF, leptin, and HDL-C were related to an increase in GM density in the left hippocampus, the insular cortex, and the left cerebellar lobule. We also observed exercise-dependent changes of diffusivity parameters in surrounding WM structures as well as in the corpus callosum. These findings suggest that weight-loss due to physical exercise in overweight to obese participants induces profound structural brain plasticity, not primarily of sensorimotor brain regions involved in physical exercise, but of regions previously reported to be structurally affected by an increased body weight and functionally implemented in gustation and cognitive processing.

Oleanolic Acid enhances the beneficial effects of preconditioning on PC12 cells

Preconditioning triggers endogenous protection against subsequent exposure to higher concentrations of a neurotoxin. In this study, we investigated whether exposure to oleanolic acid (OA) enhances the protective effects of preconditioning on PC12 cells exposed to 6-hydroxydopamine (6-OHDA). A concentration response curve was constructed using 6-OHDA (50, 150, 300, and 600 μM). The experiment consisted of 6 groups: untreated, OA only, Group 1: cells treated with 6-OHDA (50 μM) for 1 hour, Group 2: cells treated with 6-OHDA (150 μM) for 1 hour, Group 3: cells treated with 6-OHDA (50 μM) for 30 minutes followed 6 hours later by treatment with 6-OHDA (150 μM) for 30 minutes, and Group 4: cells treated as in group 3 but also received OA immediately after the second 6-OHDA treatment. Cell viability and apoptotic ratio were assessed using the MTT and Annexin V staining tests, respectively. In preconditioned cells, we found that cell viability remained high following exposure to 6-OHDA (150 μM). OA treatment enhanced the protective effects of preconditioning. Similarly, with the annexin V apoptosis test, preconditioning protected the cell and this was enhanced by OA. Therefore, preexposure of PC12 cells to low 6-OHDA concentration can protect against subsequent toxic insults of 6-OHDA and OA enhances this protection.

Aging and longevity in the simplest animals and the quest for immortality

Here we review the examples of great longevity and potential immortality in the earliest animal types and contrast and compare these to humans and other higher animals. We start by discussing aging in single-celled organisms such as yeast and ciliates, and the idea of the immortal cell clone. Then we describe how these cell clones could become organized into colonies of different cell types that lead to multicellular animal life. We survey aging and longevity in all of the basal metazoan groups including ctenophores (comb jellies), sponges, placozoans, cnidarians (hydras, jellyfish, corals and sea anemones) and myxozoans. Then we move to the simplest bilaterian animals (with a head, three body cell layers, and bilateral symmetry), the two phyla of flatworms. A key determinant of longevity and immortality in most of these simple animals is the large numbers of pluripotent stem cells that underlie the remarkable abilities of these animals to regenerate and rejuvenate themselves. Finally, we discuss briefly the evolution of the higher bilaterians and how longevity was reduced and immortality lost due to attainment of greater body complexity and cell cycle strategies that protect these complex organisms from developing tumors. We also briefly consider how the evolution of multiple aging-related mechanisms/pathways hinders our ability to understand and modify the aging process in higher organisms.

Mitohormesis: Promoting Health and Lifespan by Increased Levels of Reactive Oxygen Species (ROS)

Increasing evidence indicates that reactive oxygen species (ROS), consisting of superoxide, hydrogen peroxide, and multiple others, do not only cause oxidative stress, but rather may function as signaling molecules that promote health by preventing or delaying a number of chronic diseases, and ultimately extend lifespan. While high levels of ROS are generally accepted to cause cellular damage and to promote aging, low levels of these may rather improve systemic defense mechanisms by inducing an adaptive response. This concept has been named mitochondrial hormesis or mitohormesis. We here evaluate and summarize more than 500 publications from current literature regarding such ROS-mediated low-dose signaling events, including calorie restriction, hypoxia, temperature stress, and physical activity, as well as signaling events downstream of insulin/IGF-1 receptors, AMP-dependent kinase (AMPK), target-of-rapamycin (TOR), and lastly sirtuins to culminate in control of proteostasis, unfolded protein response (UPR), stem cell maintenance and stress resistance. Additionally, consequences of interfering with such ROS signals by pharmacological or natural compounds are being discussed, concluding that particularly antioxidants are useless or even harmful.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Methylglyoxal (MG) and cerebro-renal interaction: does long-term orally administered MG cause cognitive impairment in normal Sprague-Dawley rats?

Methylglyoxal (MG), one of the uremic toxins, is a highly reactive alpha-dicarbonyl compound. Recent clinical studies have demonstrated the close associations of cognitive impairment (CI) with plasma MG levels and presence of kidney dysfunction. Therefore, the present study aims to examine whether MG is a direct causative substance for CI development. Eight-week-old male Sprague-Dawley (SD) rats were divided into two groups: control (n = 9) and MG group (n = 10; 0.5% MG in drinking water), and fed a normal diet for 12 months. Cognitive function was evaluated by two behavioral tests (object exploration test and radial-arm maze test) in early (4–6 months of age) and late phase (7–12 months of age). Serum MG was significantly elevated in the MG group (495.8 ± 38.1 vs. 244.8 ± 28.2 nM; p < 0.001) at the end of study. The groups did not differ in cognitive function during the course of study. No time-course differences were found in oxidative stress markers between the two groups, while, antioxidants such as glutathione peroxidase and superoxide dismutase activities were significantly increased in the MG group compared to the control. Long-term MG administration to rats with normal kidney function did not cause CI. A counter-balanced activation of the systemic anti-oxidant system may offset the toxicity of MG in this model. Pathogenetic significance of MG for CI requires further investigation.

Interaction between serum BDNF and aerobic fitness predicts recognition memory in healthy young adults

Convergent evidence from human and non-human animal studies suggests aerobic exercise and increased aerobic capacity may be beneficial for brain health and cognition. It is thought growth factors may mediate this putative relationship, particularly by augmenting plasticity mechanisms in the hippocampus, a brain region critical for learning and memory. Among these factors, glucocorticoids, brain derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF), hormones that have considerable and diverse physiological importance, are thought to effect normal and exercise-induced hippocampal plasticity. Despite these predictions, relatively few published human studies have tested hypotheses that relate exercise and fitness to the hippocampus, and none have considered the potential links to all of these hormonal components. Here we present cross-sectional data from a study of recognition memory; serum BDNF, cortisol, IGF-1, and VEGF levels; and aerobic capacity in healthy young adults. We measured circulating levels of these hormones together with performance on a recognition memory task, and a standard graded treadmill test of aerobic fitness. Regression analyses demonstrated BDNF and aerobic fitness predict recognition memory in an interactive manner. In addition, IGF-1 was positively associated with aerobic fitness, but not with recognition memory. Our results may suggest an exercise adaptation-related change in the BDNF dose-response curve that relates to hippocampal memory.

Adaptive response to hydrogen peroxide in yeast: induction, time course, and relationship to dose-response models

The assay for trp5 gene conversion and ilv1-92 reversion in Saccharomyces cerevisiae strain D7 was used to characterize the induction of an adaptive response by hydrogen peroxide (H(2)O(2)). Effects of a small priming dose on the genotoxic effects of a larger challenge dose were measured in exponential cultures and in early stationary phase. An adaptive response, indicated by smaller convertant and revertant frequencies after the priming dose, occurred at lower priming and challenge doses in young, well-aerated cultures. Closely spaced priming doses from 0.000975 to 2 mM, followed by a 1 mM challenge, showed that the induction of the adaptive response is biphasic. In exponential cultures it was maximal with a priming dose of 0.125-0.25 mM. Very small priming doses were insufficient to induce the adaptive response, whereas higher doses contributed to damage. A significant adaptive response was detected when the challenge dose was administered 10-20 min after the priming exposure. It was fully expressed within 45 min, and the yeast began to return to the nonadapted state after 4-6 hr. Because of the similarity of the biphasic induction to hormetic curves and the proposal that adaptive responses are a manifestation of hormesis, we evaluated whether the low doses of H(2)O(2) that induce the adaptive response show a clear hormetic response without a subsequent challenge dose. Hormesis was not evident, but there was an apparent threshold for genotoxicity at or slightly below 0.125 mM. The results are discussed with respect to linear, threshold, and hormesis dose-response models.

Developmental exposure to decabrominated diphenyl ether (BDE-209): effects on sperm oxidative stress and chromatin DNA damage in mouse offspring

Polybrominated diphenyl ethers (PBDEs) are used as brominated flame retardants and have been found in human milk in recent years. This study investigates whether prenatal exposure to decabrominated diphenyl ether (BDE-209) induces sperm dysfunction in male offspring. Pregnant CD-1 mice were gavaged once daily with corn oil (control), 10, 500, and 1500 mg kg(-1) body weight of BDE-209 from day 0 of gestation to day 17. The outcomes of male reproductive parameters were assessed on postnatal day 71. Anogenital distance, sperm-head abnormalities, and testicular histopathology were significantly affected in male offspring prenatally exposed to 1500 mg kg(-1). Significant increases in the tendency for sperm DNA denaturation (αT) induction and the DNA fragmentation index (DFI) were found in those exposed to 10, 500, and 1500 mg kg(-1) (P < 0.05). We observed a significant increase of sperm hydrogen peroxide (H(2)O(2)) generation in the 10 and 1500 mg/kg/day groups compared to the control group (P < 0.05). Although our findings suggested that the mechanisms underlying BDE-209-induced sperm DNA damage and H(2)O(2) generation might not be represented as a dose-response relationship, we found that the greater the excess production of sperm H(2)O(2), the greater the sperm αT (r = 0.65, P = 0.0155) and DFI (r = 0.53, P = 0.002). In conclusion, developmental exposure to BDE-209 induced sperm-head abnormality, oxidative stress, chromatin DNA damage, and testicular histopathological changes. These findings suggest that BDE-209-induced male reproductive effects might involve the formation of sperm H(2)O(2) which attacks nucleic acids via H(2)O(2) generation.

Hormesis in aging and neurodegeneration-a prodigy awaiting dissection

Hormesis describes the drug action of low dose stimulation and high dose inhibition. The hormesis phenomenon has been observed in a wide range of biological systems. Although known in its descriptive context, the underlying mode-of-action of hormesis is largely unexplored. Recently, the hormesis concept has been receiving increasing attention in the field of aging research. It has been proposed that within a certain concentration window, reactive oxygen species (ROS) or reactive nitrogen species (RNS) could act as major mediators of anti-aging and neuroprotective processes. Such hormetic phenomena could have potential therapeutic applications, if properly employed. Here, we review the current theories of hormetic phenomena in regard to aging and neurodegeneration, with the focus on its underlying mechanism. Facilitated by a simple mathematical model, we show for the first time that ROS-mediated hormesis can be explained by the addition of different biomolecular reactions including oxidative damage, MAPK signaling and autophagy stimulation. Due to their divergent scales, the optimal hormetic window is sensitive to each kinetic parameter, which may vary between individuals. Therefore, therapeutic utilization of hormesis requires quantitative characterizations in order to access the optimal hormetic window for each individual. This calls for a personalized medicine approach for a longer human healthspan.

Phenolphthalein induces centrosome amplification and tubulin depolymerization in vitro

Aneuploidy is a major cause of human reproductive failure and plays a large role in cancer. Phenolphthalein (PHT) induces tumors in rodents but its primary mechanism does not seem to be DNA damage. In heterozygous TSG-p53(®) mice, PHT induces lymphomas and also micronuclei (MN), many containing kinetochores (K), implying chromosome loss (aneuploidy). The induction of aneuploidy would be compatible with the loss of the normal p53 gene seen in the lymphomas. In this study, we confirm PHT's aneugenicity and determine the aneugenic mechanism of PHT by combining traditional genetic toxicology assays with image and flow cytometry methods. The data revealed that PHT induces tubulin polymerization abnormalities and deregulates the centrosome duplication cycle causing centrosome amplification. We also show that one of the consequences of these events is apoptosis.

Dietary oils mediate cortisol kinetics and the hepatic mRNA expression profile of stress-responsive genes in gilthead sea bream (Sparus aurata) exposed to crowding stress. Implications on energy homeostasis and stress susceptibility

Juveniles of gilthead sea bream were fed with plant protein-based diets with fish oil (FO diet) or vegetable oils (66VO diet) as dietary lipid sources. No differences in growth performance were found between both groups, and fish with an average body mass of 65-70 g were crowded (90-100 kg/m(3)) to assess the stress response within the 72 h after the onset of stressor. The rise in plasma cortisol and glucose levels was higher in stressed fish of group 66VO (66VO-S) than in FO group (FO-S), but the former stressed group regained more quickly the cortisol resting values of the corresponding non-stressed diet group. The cell-tissue repair response represented by derlin-1, 75 kDa glucose-regulated protein and 170 kDa glucose-regulated protein was triggered at a lower level in 66VO-S than in FO-S fish. This occurred in concert with a long-lasting up-regulation of glucocorticoid receptors, antioxidant enzymes, enzyme subunits of the mitochondrial respiratory chain, and enzymes involved in tissue fatty acid uptake and β-oxidation. This gene expression pattern allows a metabolic phenotype that is prone to "high power" mitochondria, which would support the replacement of fish oil with vegetable oils when theoretical requirements in essential fatty acids for normal growth are met by diet.

Hormesis, cell death, and regenerative medicine for neurode-generative diseases

Although the adult human brain has a small number of neural stem cells, they are insufficient to repair the damaged brain to achieve significant functional recovery for neurodegenerative diseases and stroke. Stem cell therapy, by either enhancing endogenous neurogenesis, or transplanting stem cells, has been regarded as a promising solution. However, the harsh environment of the diseased brain posts a severe threat to the survival and correct differentiation of those new stem cells. Hormesis (or preconditioning, stress adaptation) is an adaptation mechanism by which cells or organisms are potentiated to survive an otherwise lethal condition, such as the harsh oxidative stress in the stroke brain. Stem cells treated by low levels of chemical, physical, or pharmacological stimuli have been shown to survive better in the neurodegenerative brain. Thus combining hormesis and stem cell therapy might improve the outcome for treatment of these diseases. In addition, since the cell death patterns and their underlying molecular mechanism may vary in different neurodegenerative diseases, even in different progression stages of the same disease, it is essential to design a suitable and optimum hormetic strategy that is tailored to the individual patient.

Effects of polyphenols on brain ageing and Alzheimer's disease: focus on mitochondria

The global trend of the phenomenon of population ageing has dramatic consequences on public health and the incidence of neurodegenerative diseases. Physiological changes that occur during normal ageing of the brain may exacerbate and initiate pathological processes that may lead to neurodegenerative disorders, especially Alzheimer's disease (AD). Hence, the risk of AD rises exponentially with age. While there is no cure currently available, sufficient intake of certain micronutrients and secondary plant metabolites may prevent disease onset. Polyphenols are highly abundant in the human diet, and several experimental and epidemiological evidences indicate that these secondary plant products have beneficial effects on AD risks. This study reviews current knowledge on the potential of polyphenols and selected polyphenol-rich diets on memory and cognition in human subjects, focusing on recent data showing in vivo efficacy of polyphenols in preventing neurodegenerative events during brain ageing and in dementia. Concentrations of polyphenols in animal brains following oral administration have been consistently reported to be very low, thus eliciting controversial discussion on their neuroprotective effects and potential mechanisms. Whether polyphenols exert any direct antioxidant effects in the brain or rather act by evoking alterations in regulatory systems of the brain or even the body periphery is still unclear. To understand the mechanisms behind the protective abilities of polyphenol-rich foods, an overall understanding of the biotransformation of polyphenols and identification of the various metabolites arising in the human body is also urgently needed.

Effects of aging and caloric restriction on brainstem satiety center signals in rats

Age-related increases of body weight and adiposity, indicating dysregulation of food intake/energy expenditure, can be prevented in rodents by long-term 40% caloric restriction. The dorsal vagal complex (DVC), the brainstem center mediating the satiety reflex, has recently emerged as a determinant effector of long-term feeding adaptation. To study the effects of aging and caloric restriction on satiety circuits, leptin and brain-derived neurotrophic factor (BDNF) signaling systems were studied in 2- and 19-month-old ad libitum-fed (AL) and 19-month-old calorie-restricted (CR) rats. Age-induced hyperleptinemia in AL rats was correlated with elevated DVC BDNF immunoreactive concentrations and satiety threshold stability, suggesting functional desensitization of the DVC to these signals. To better understand this phenomenon, mRNA levels of receptor and post-receptor signaling effectors were measured by real-time RT-PCR. Aging selectively increased BDNF receptors and suppressor of cytokine signaling-3 (SOCS-3) mRNA levels. Caloric restriction prevented age-related increases of serum leptin, DVC BDNF and SOCS-3 mRNA levels, but not those of BDNF receptors. In CR rats, prevention of leptin resistance-promoting SOCS-3 induction was also observed at the protein level. This study suggests that leptin post-receptor targets and BDNF signaling play a role in the establishment of age-related DVC dysfunction.