Aberrant insulin receptor signaling and amino acid homeostasis as a major cause of oxidative stress in aging

In vivo 'turn on' fluorescence detection of free cysteine in zebrafish kidney and liver

Cysteine is directly associated with a wide range of biological processes. Besides its essential role in protein synthesis, cysteine undergoes a variety of post-translational modifications which modulate several physiological processes. Dysregulated cysteine metabolism is associated with several neurodegenerative disorders. Accordingly, restoring cysteine balance has therapeutic benefits. It is therefore essential to detect the presence of endogenous free cysteine in order to understand different physiological modes of action inside the cell. Here, a carbazole-pyridoxal conjugate system (CPLC) has been developed to detect endogenous free cysteine in the liver and kidney of an adult zebrafish. In consequence, we have also determined the fluorescence intensity statistics of zebrafish kidney and liver images. CPLC interacts in a very fascinating way with two cysteine molecules through chemodosimetric and chemosensing approaches which are conclusively proved by different spectroscopic analyses (UV-vis, fluorescence, NMR) and theoretical calculations (DFT). The detection limit of CPLC towards cysteine is 0.20 μM. Moreover, this preliminary experiment has been done using HuH-7 cell line to check the permeability of CPLC, interaction with cysteine intracellularly, and assessment of the toxicity of CPLC, if any, before performing details in-vivo experiments in zebrafish model.

Potential Roles of Glucagon-Like Peptide-1 and Its Analogues in Dementia Targeting Impaired Insulin Secretion and Neurodegeneration

Dementia is a chronic, irreversible condition marked by memory loss, cognitive decline, and mental instability. It is clinically related to various progressive neurological diseases, including Parkinson’s disease, Alzheimer’s disease, and Huntington’s. The primary cause of neurological disorders is insulin desensitization, demyelination, oxidative stress, and neuroinflammation accompanied by various aberrant proteins such as amyloid-β deposits, Lewy bodies accumulation, tau formation leading to neurofibrillary tangles. Impaired insulin signaling is directly associated with amyloid-β and α-synuclein deposition, as well as specific signaling cascades involved in neurodegenerative diseases. Insulin dysfunction may initiate various intracellular signaling cascades, including phosphoinositide 3-kinase (PI3K), c-Jun N-terminal kinases (JNK), and mitogen-activated protein kinase (MAPK). Neuronal death, inflammation, neuronal excitation, mitochondrial malfunction, and protein deposition are all influenced by insulin. Recent research has focused on GLP-1 receptor agonists as a potential therapeutic target. They increase glucose-dependent insulin secretion and are beneficial in neurodegenerative diseases by reducing oxidative stress and cytokine production. They reduce the deposition of abnormal proteins by crossing the blood-brain barrier. The purpose of this article is to discuss the role of insulin dysfunction in the pathogenesis of neurological diseases, specifically dementia. Additionally, we reviewed the therapeutic target (GLP-1) and its receptor activators as a possible treatment of dementia.

Homer signaling pathways as effective therapeutic targets for ischemic and traumatic brain injuries and retinal lesions

Ischemic and traumatic insults to the central nervous system account for most serious acute and fatal brain injuries and are usually characterized by primary and secondary damage. Secondary damage presents the greatest challenge for medical staff; however, there are currently few effective therapeutic targets for secondary damage. Homer proteins are postsynaptic scaffolding proteins that have been implicated in ischemic and traumatic insults to the central nervous system. Homer signaling can exert either positive or negative effects during such insults, depending on the specific subtype of Homer protein. Homer 1b/c couples with other proteins to form postsynaptic densities, which form the basis of synaptic transmission, while Homer1a expression can be induced by harmful external factors. Homer 1c is used as a unique biomarker to reveal alterations in synaptic connectivity before and during the early stages of apoptosis in retinal ganglion cells, mediated or affected by extracellular or intracellular signaling or cytoskeletal processes. This review summarizes the structural features, related signaling pathways, and diverse roles of Homer proteins in physiological and pathological processes. Upregulating Homer1a or downregulating Homer1b/c may play a neuroprotective role in secondary brain injuries. Homer also plays an important role in the formation of photoreceptor synapses. These findings confirm the neuroprotective effects of Homer, and support the future design of therapeutic drug targets or gene therapies for ischemic and traumatic brain injuries and retinal disorders based on Homer proteins.

SG1002 and Catenated Divalent Organic Sulfur Compounds as Promising Hydrogen Sulfide Prodrugs

Significance: Sulfur has a critical role in protein structure/function and redox status/signaling in all living organisms. Although hydrogen sulfide (H2S) and sulfane sulfur (SS) are now recognized as central players in physiology and pathophysiology, the full scope and depth of sulfur metabolome's impact on human health and healthy longevity has been vastly underestimated and is only starting to be grasped. Since many pathological conditions have been related to abnormally low levels of H2S/SS in blood and/or tissues, and are amenable to treatment by H2S supplementation, development of safe and efficacious H2S donors deserves to be undertaken with a sense of urgency; these prodrugs also hold the promise of becoming widely used for disease prevention and as antiaging agents. Recent Advances: Supramolecular tuning of the properties of well-known molecules comprising chains of sulfur atoms (diallyl trisulfide [DATS], S8) was shown to lead to improved donors such as DATS-loaded polymeric nanoparticles and SG1002. Encouraging results in animal models have been obtained with SG1002 in heart failure, atherosclerosis, ischemic damage, and Duchenne muscular dystrophy; with TC-2153 in Alzheimer's disease, schizophrenia, age-related memory decline, fragile X syndrome, and cocaine addiction; and with DATS in brain, colon, gastric, and breast cancer. Critical Issues: Mode-of-action studies on allyl polysulfides, benzyl polysulfides, ajoene, and 12 ring-substituted organic disulfides and thiosulfonates led several groups of researchers to conclude that the anticancer effect of these compounds is not mediated by H2S and is only modulated by reactive oxygen species, and that their central model of action is selective protein S-thiolation. Future Directions: SG1002 is likely to emerge as the H2S donor of choice for acquiring knowledge on this gasotransmitter's effects in animal models, on account of its unique ability to efficiently generate H2S without byproducts and in a slow and sustained mode that is dose independent and enzyme independent. Efficient tuning of H2S donation characteristics of DATS, dibenzyl trisulfide, and other hydrophobic H2S prodrugs for both oral and parenteral administration will be achieved not only by conventional structural modification of a lead molecule but also through the new "supramolecular tuning" paradigm.

Follicle Stimulating Hormone Inhibits the Expression of p53 Up-Regulated Modulator of Apoptosis Induced by Reactive Oxygen Species Through PI3K/Akt in Mouse Granulosa Cells

In mammalian ovaries, follicular atresia occurs periodically and destroys almost all the follicles in the ovary. Follicle-stimulating hormone (FSH) acts as the primary survival factor during follicular atresia by preventing apoptosis in granulosa cells (GCs). Many studies have demonstrated that oxidative stress-induced apoptosis is a main cause of follicular atresia. Reactive oxygen species (ROS)-induced GCs apoptosis is regulated by a variety of signaling pathways involving numerous genes and transcription factors. Therefore, we examined whether FSH inhibits the expression of p53 up-regulated modulator of apoptosis (PUMA) induced by reactive oxygen species (ROS) through phosphoinositide 3-kinase (PI3K) / protein kinase B (AKT) in mouse GCs. In vivo study: thirty-two-mice were randomly assigned to four groups and given FSH. We found that FSH can inhibit the 3-nitropropionic acid (3-NP) induced apoptosis and PUMA expression in mRNA level. Moreover, In vitro experiment, we found that FSH can inhibit the H(2)O(2)-induced apoptosis and PUMA expression in mRNA level. Additionally, we also found that PI3K/AKT inhibitor LY294002 abolished the downregulation of PUMA mRNA by FSH in vitro, In conclusion, FSH inhibit the expression of PUMA induced by ROS through PI3K/AKT pathway in vivo and vitro.

Roles of poly (ADP-ribose) polymerase 1 activation and cleavage in induction of multi-oocyte ovarian follicles in the mouse by 3-nitropropionic acid

3-nitropropionic acid (3-NPA) is known to be a mitochondrial toxin produced by plants and fungi, which may produce DNA damage in cells. However, studies of its reproductive toxicology are lacking. We know that poly(ADP-ribose) polymerase (PARP) plays an important role in a large variety of physiological processes and is involved in DNA repair pathways. The present study was therefore aimed at exploring the involvement of PARP-1 activation and cleavage after 3-NPA stimulation in female mice. We observed an increased number of atretic follicles and multi-oocyte follicles (MOFs) after treatment with 3-NPA and serum concentrations of 17β-oestradiol and progesterone were significantly reduced. Our results provide evidence that PARP-1 cleavage and activational signals are involved in pathological ovarian processes stimulated by 3-NPA. In addition, total superoxide dismutase, glutathione peroxidase and catalase activities were significantly increased, whereas succinate dehydrogenase was decreased in a dose-dependent manner. Results from our in vitro study similarly indicated that 3-NPA inhibited the proliferation of mouse granulosa cells and increased apoptosis in a dose-dependent manner. In summary, 3-NPA induces granulosa cell apoptosis, follicle atresia and MOFs in the ovaries of female mice and causes oxidative stress so as to disrupt endogenous hormonal systems, possibly acting through PARP-1 signalling.

Genetic Ablation of the Cystine Transporter xCT in PDAC Cells Inhibits mTORC1, Growth, Survival, and Tumor Formation via Nutrient and Oxidative Stresses

Although chemoresistance remains a primary challenge in the treatment of pancreatic ductal adenocarcinoma (PDAC), exploiting oxidative stress might offer novel therapeutic clues. Here we explored the potential of targeting cystine/glutamate exchanger (SLC7A11/xCT), which contributes to the maintenance of intracellular glutathione (GSH). Genomic disruption of xCT via CRISPR-Cas9 was achieved in two PDAC cell lines, MiaPaCa-2 and Capan-2, and xCT-KO clones were cultivated in the presence of N-acetylcysteine. Although several cystine/cysteine transporters have been identified, our findings demonstrate that, in vitro, xCT plays the major role in intracellular cysteine balance and GSH biosynthesis. As a consequence, both xCT-KO cell lines exhibited amino acid stress with activation of GCN2 and subsequent induction of ATF4, inhibition of mTORC1, proliferation arrest, and cell death. Tumor xenograft growth was delayed but not suppressed in xCT-KO cells, which indicated both the key role of xCT and also the presence of additional mechanisms for cysteine homeostasis in vivo. Moreover, rapid depletion of intracellular GSH in xCT-KO cells led to accumulation of lipid peroxides and cell swelling. These two hallmarks of ferroptotic cell death were prevented by vitamin E or iron chelation. Finally, in vitro pharmacologic inhibition of xCT by low concentrations of erastin phenocopied xCT-KO and potentiated the cytotoxic effects of both gemcitabine and cisplatin in PDAC cell lines. In conclusion, our findings strongly support that inhibition of xCT, by its dual induction of nutritional and oxidative cellular stresses, has great potential as an anticancer strategy. SIGNIFICANCE: The cystine/glutamate exchanger xCT is essential for amino acid and redox homeostasis and its inhibition has potential for anticancer therapy by inducing ferroptosis.

Actomyosin contraction during cellularization is regulated in part by Src64 control of Actin 5C protein levels

Src64 is required for actomyosin contraction during cellularization of the Drosophila embryonic blastoderm. The mechanism of actomyosin ring constriction is poorly understood even though a number of cytoskeletal regulators have been implicated in the assembly, organization, and contraction of these microfilament rings. How these cytoskeletal processes are regulated during development is even less well understood. To investigate the role of Src64 as an upstream regulator of actomyosin contraction, we conducted a proteomics screen to identify proteins whose expression levels are controlled by src64. Global levels of actin are reduced in src64 mutant embryos. Furthermore, we show that reduction of the actin isoform Actin 5C causes defects in actomyosin contraction during cellularization similar to those caused by src64 mutation, indicating that a relatively high level of Actin 5C is required for normal actomyosin contraction and furrow canal structure. However, reduction of Actin 5C levels only slows down actomyosin ring constriction rather than preventing it, suggesting that src64 acts not only to modulate actin levels, but also to regulate the actomyosin cytoskeleton by other means.

Neuroprotective effects of berberine on recognition memory impairment, oxidative stress, and damage to the purinergic system in rats submitted to intracerebroventricular injection of streptozotocin

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disease. The present study investigated the effects of 50 and 100 mg/kg berberine (BRB) on recognition memory, oxidative stress, and purinergic neurotransmission, in a model of sporadic dementia of the Alzheimer's type induced by intracerebroventricular (ICV) injection of streptozotocin (STZ) in rats. Rats were submitted to ICV-STZ 3 mg/kg or saline, and 3 days later, were started on a treatment of BRB or saline for 21 days. The results demonstrated that BRB was effective in protecting against memory impairment, increased reactive oxygen species, and the subsequent increase in protein and lipid oxidation in the cerebral cortex and hippocampus, as well as δ-aminolevulinate dehydratase inhibition in the cerebral cortex. Moreover, the decrease in total thiols, and the reduced glutathione and glutathione S-transferase activity in the cerebral cortex and hippocampus of ICV-STZ rats, was prevented by BRB treatment. Besides an antioxidant effect, BRB treatment was capable of preventing decreases in ecto-nucleoside triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase (EC-5'-Nt), and adenosine deaminase (ADA) activities in synaptosomes of the cerebral cortex and hippocampus. Thus, our data suggest that BRB exerts a neuroprotective effect on recognition memory, as well as on oxidative stress and oxidative stress-related damage, such as dysfunction of the purinergic system. This suggests that BRB may act as a promising multipotent agent for the treatment of AD.

The effect of aging on the autophagic and heat shock response in human peripheral blood mononuclear cells

Autophagy is a lysosome degradation pathway through which damaged organelles and macromolecules are degraded within the cell. A decrease in activity of the autophagic process has been linked to several age-associated pathologies, including triglyceride accumulation, mitochondrial dysfunction, muscle degeneration, and cardiac malfunction. Here, we examined the differences in the autophagic response using autophagy-inducer rapamycin (Rapa) in peripheral blood mononuclear cells (PBMCs) from young (21.8 ± 1.9 years) and old (64.0 ± 3.7 years) individuals. Furthermore, we tested the interplay between the heat shock response and autophagy systems. Our results showed a significant increase in LC3-II protein expression in response to Rapa treatment in young but not in old individuals. This was associated with a decreased response in MAP1LC3B mRNA levels, but not SQSTM1/p62. Furthermore, HSPA1A mRNA was upregulated only in young individuals, despite no differences in HSP70 protein expression. The combined findings suggest a suppressed autophagic response following Rapa treatment in older individuals.

Thymoquinone protects human retinal pigment epithelial cells against hydrogen peroxide induced oxidative stress and apoptosis

Oxidative stress in retinal pigment epithelium (RPE) cells may contribute to the progression of age-related macular degeneration. Thymoquinone (TQ), an active component derived from Nigella sativa, possesses antioxidative effect. However, the role of TQ in RPE cells under oxidative stress condition remains unclear. The present study aimed to examine the protective effect of TQ against hydrogen peroxide (H₂ O₂ )-induced oxidative stress in human RPE cells. Our results showed that TQ improved the cell viability and apoptosis in H₂ O₂ -induced ARPE cells. We also found that the levels of reactive oxygen species and malondialdehyde induced by H₂ O₂ were reduced after the pretreatment of TQ. In addition, the inhibitory effect of H₂ O₂ on the glutathione (GSH) level and superoxide dismutase activity was markedly attenuated by TQ pretreatment. Moreover, TQ enhanced the activation of Nrf2/heme oxygenase 1 (HO-1) signaling pathway in H₂ O₂ -induced ARPE cells. Knockdown of Nrf2 abolished the protective effect of TQ on H₂ O₂ -induced oxidative damage. These results suggested that TQ protected ARPE cells from H₂ O₂ -induced oxidative stress and apoptosis via the Nrf2/HO-1 signaling pathway.

Cysteine Metabolism in Neuronal Redox Homeostasis

Besides its essential role in protein synthesis, cysteine plays vital roles in redox homeostasis, being a component of the major antioxidant glutathione (GSH) and a potent antioxidant by itself. In addition, cysteine undergoes a variety of post-translational modifications that modulate several physiological processes. It is becoming increasingly clear that redox-modulated events play important roles not only in peripheral tissues but also in the brain where cysteine disposition is central to these pathways. Dysregulated cysteine metabolism is associated with several neurodegenerative disorders. Accordingly, restoration of cysteine balance has therapeutic benefits. This review discusses metabolic signaling pathways pertaining to cysteine disposition in the brain under normal and pathological conditions, highlighting recent findings on cysteine metabolism during aging and in neurodegenerative conditions such as Huntington's disease (HD) and molybdenum cofactor (MoCo) deficiency (MoCD) among others.

Intranasal Insulin Administration Ameliorates Streptozotocin (ICV)-Induced Insulin Receptor Dysfunction, Neuroinflammation, Amyloidogenesis, and Memory Impairment in Rats

Alzheimer's disease (AD) is associated with reduced insulin level and impairment of insulin receptor (IR) signaling in the brain, which correlates to amyloid pathology, neuroinflammation, and synaptic neurotoxicity. Clinical studies show that intranasal insulin improves memory in AD patients without peripheral hypoglycemia. However, neuroprotective molecular mechanism of the beneficial effect of intranasal insulin in AD pathology is unexplored. Therefore, we investigated the role of intranasal insulin on intracerebroventricular (ICV) streptozotocin (STZ)-induced memory impairment in rats as evaluated in the Morris water maze test. STZ (ICV) treated rats had shown memory impairment along with a significant decrease in IR signaling molecules (IR, pIRS-1, pAkt, and pGSK-3α/β expression) and IDE expression in both hippocampus and cerebral cortex. Intranasal insulin delivery prevented these changes. Moreover, intranasal insulin was found to inhibit significantly glial cell activation (GFAP and Iba-1 expression), neuroinflammation (COX-2 expression, NFκB translocation, TNF-α, and IL-10 level) and amyloidogenic protein expression (BACE-1 and Aβ_1-42 expression) in STZ (ICV)-injected rats. STZ (ICV)-induced caspase activation and postsynaptic neurotoxicity were also prevented by treatment with intranasal insulin. Our findings reveal that insulin has the neuroprotective effect and clearly signifies the potential use of intranasal insulin delivery for the treatment of AD. Graphical Abstract Neuroprotective effects of intranasal insulin administration on streptozotocin (ICV)-induced memory impairment in rats.

OGG1 is essential in oxidative stress induced DNA demethylation

DNA demethylation is an essential cellular activity to regulate gene expression; however, the mechanism that triggers DNA demethylation remains unknown. Furthermore, DNA demethylation was recently demonstrated to be induced by oxidative stress without a clear molecular mechanism. In this manuscript, we demonstrated that 8-oxoguanine DNA glycosylase-1 (OGG1) is the essential protein involved in oxidative stress-induced DNA demethylation. Oxidative stress induced the formation of 8-oxoguanine (8-oxoG). We found that OGG1, the 8-oxoG binding protein, promotes DNA demethylation by interacting and recruiting TET1 to the 8-oxoG lesion. Downregulation of OGG1 makes cells resistant to oxidative stress-induced DNA demethylation, while over-expression of OGG1 renders cells susceptible to DNA demethylation by oxidative stress. These data not only illustrate the importance of base excision repair (BER) in DNA demethylation but also reveal how the DNA demethylation signal is transferred to downstream DNA demethylation enzymes.

Chronic Exposure to Diquat Causes Reproductive Toxicity in Female Mice

Diquat is a bipyridyl herbicide that has been widely used as a model chemical for in vivo studies of oxidative stress due to its generation of superoxide anions, and cytotoxic effects. There is little information regarding the toxic effects of diquat on the female reproductive system, particularly ovarian function. Thus, we investigated the reproductive toxic effects of diquat on female mice. Chronic exposure to diquat reduced ovary weights, induced ovarian oxidative stress, resulted in granulosa cell apoptosis, and disrupted oocyte developmental competence, as shown by reactive oxygen species (ROS) accumulation, decreased polar body extrusion rates and increased apoptosis-related genes expression. Additionally, after diquat treatment, the numbers of fetal mice and litter sizes were significantly reduced compared to those of control mice. Thus, our results indicated that chronic exposure to diquat induced reproductive toxicity in female mice by promoting the ROS production of gruanousa cells and ooctyes, impairing follicle development, inducing apoptosis, and reducing oocyte quality. In conclusion, our findings indicate that diquat can be used as a potent and efficient chemical for in vivo studies of female reproductive toxicity induced by oxidative stress. Moreover, the findings from this study will further enlarge imitative research investigating the effect of ovarian damage induced by oxidative stress on reproductive performance and possible mechanisms of action in large domestic animals.

Puerarin attenuates learning and memory impairments and inhibits oxidative stress in STZ-induced SAD mice

Puerarin (PUE), an isoflavone purified from the root of Pueraria lobata (Chinese herb), has been reported to attenuate learning and memory impairments in the transgenic mouse model of Alzheimer's disease (AD). In the present study, we tested PUE in a sporadic AD (SAD) mouse model which was induced by the intracerebroventricular injection of streptozotocin (STZ). The mice were administrated PUE (25, 50, or 100mg/kg/d) for 28 days. Learning and memory abilities were assessed by the Morris water maze test. After behavioral test, the biochemical parameters of oxidative stress (glutathione peroxidase (GSH-Px), superoxide dismutases (SOD), and malondialdehyde (MDA)) were measured in the cerebral cortex and hippocampus. The SAD mice exhibited significantly decreased learning and memory ability, while PUE attenuated these impairments. The activities of GSH-Px and SOD were decreased while MDA was increased in the SAD animals. After PUE treatment, the activities of GSH-Px and SOD were elevated, and the level of MDA was decreased. The middle dose PUE was more effective than others. These results indicate that PUE attenuates learning and memory impairments and inhibits oxidative stress in STZ-induced SAD mice. PUE may be a promising therapeutic agent for SAD.

Effect of cysteine-rich whey protein (immunocal®) supplementation in combination with resistance training on muscle strength and lean body mass in non-frail elderly subjects: a randomized, double-blind controlled study

OBJECTIVES

The purpose of the present study was to examine the effect of a cysteine-rich whey protein (Immunocal®) supplementation in combination with resistance training on muscle strength and lean body mass (LBM) in elderly individuals. We hypothesized that the cysteine-rich whey protein (Immunocal®) group would experience a greater increase in muscle strength and lean body mass versus the control group (casein).

DESIGN

Randomized double-blind controlled intervention study.

SETTING

Institut de Recherches Cliniques de Montréal in Montreal, Canada.

PARTICIPANTS

Ninety-nine non-frail elderly subjects were recruited.

INTERVENTION

Participants were randomly assigned into two groups. The experimental group received a cysteine-rich whey protein isolate (Immunocal®) (20 g/day) and the control group received casein (20 g/day) during a 135-day period. In addition, both groups performed the same resistance training program (3 times per week).

MEASUREMENTS

Body composition (DXA) and muscle strength (leg press) were measured.

RESULTS

Of the 99 recruited participants, 84 completed the 135-day study period. Of these, 67 subjects (33 in the casein group and 34 in the Immunocal® group) complied and used at least 80 % of the study product and completed at least 80 % of their training sessions. Results in this selected group show an increase in all three muscle strength variables (absolute, normalized by BW and by LBM) by 31.0 %, 30.9 % and 30.0 %, respectively in the casein group as well as 39.3 %, 39.9 % and 43.3 %, respectively in the Immunocal® group after the intervention (p < 0.05). The increases in muscle strength favored Immunocal® versus casein by approximately 10 % when expressed in kg per kg BW and in kg per kg LBM (p < 0.05). No significant changes were found between pre-and-post intervention in both groups for total LBM.

CONCLUSIONS

Our findings showed increases in muscle strength in both groups after resistance training, however, significant additional increases were observed in muscle strength with the addition of a cysteine-rich whey protein (Immunocal®) versus casein.

Metabolome-wide association study of phenylalanine in plasma of common marmosets

Little systematic knowledge exists concerning the impacts of cumulative lifelong exposure, termed the exposome, on requirements for nutrients. Phenylalanine (Phe) is an essential dietary amino acid with an aromatic ring structure similar to endogenous metabolites, dietary compounds and environmental agents. Excess plasma Phe in genetic disease or nutritional deficiency of Phe has adverse health consequences. In principle, structurally similar chemicals interfering with Phe utilization could alter Phe requirement at an individual level. As a strategy to identify components of the exposome that could interfere with Phe utilization, we tested for metabolites correlating with Phe concentration in plasma of a non-human primate species, common marmosets (Callithrix jacchus). The results of tests for more than 5,000 chemical features detected by high-resolution metabolomics showed 17 positive correlations with Phe metabolites and other amino acids. Positive and negative correlations were also observed for 33 other chemicals, which included matches to endogenous metabolites and dietary, microbial and environmental chemicals in database searches. Chemical similarity analysis showed many of the matches had high structural similarity to Phe. Together, the results show that chemicals in marmoset plasma could impact Phe utilization. Such chemicals could contribute to early lifecycle developmental disorders when neurological development is vulnerable to Phe levels.

Protection of streptozotocin induced insulin receptor dysfunction, neuroinflammation and amyloidogenesis in astrocytes by insulin

Impaired insulin signaling, amyloid pathology and neuroinflammation are closely associated with neurodegenerative disorder like Alzheimer's disease (AD). Our earlier studies showed that intracerebroventricular streptozotocin (STZ) induces insulin receptor (IR) signaling defect in the hippocampus, which is associated with memory impairment in rats. Astrocytes are the most abundant cells in the brain and play a major role in neuroinflammation. However, involvement of astrocytes in STZ induced IR dysfunction has not received much attention. Therefore, the present study was planned to explore the effect of STZ on IR signaling, proinflammatory markers and amyloidogenesis in rat astrocytoma cell line, (C6). STZ (100 μM) treatment in astrocytes (n = 3) for 24 h, resulted significant decrease in IR mRNA and protein expression, phosphorylation of IRS-1, Akt, GSK-3α and GSK-3β (p < 0.01). Further STZ induced amyloidogenic protein expression as evidenced by the increase in APP, BACE-1 and Aβ1-42 expression (p < 0.05) in astrocytes. STZ also significantly induced astrocytes activation as evidenced by increased expression of GFAP and p-P38 MAPK (p < 0.05). STZ treatment caused enhanced translocation of p65 NF-kB, triggered over expression of TNF-α, IL-1β, COX-2, oxidative/nitrosative stress and caspase activation (p < 0.05) in astrocytes. Insulin (25-100 nM) pretreatment (n = 3) significantly prevented changes in IR signaling, amyloidogenic protein expression and levels of proinflammatory markers (p < 0.05) in STZ treated astroglial cells. In the present study, the protective effect of insulin suggests that, IR dysfunction along with amyloidogenesis and neuroinflammation may have played a major role in STZ induced toxicity in astrocytes which are relevant to AD pathology.

Agmatine improves cognitive dysfunction and prevents cell death in a streptozotocin-induced Alzheimer rat model

PURPOSE

Alzheimer's disease (AD) results in memory impairment and neuronal cell death in the brain. Previous studies demonstrated that intracerebroventricular administration of streptozotocin (STZ) induces pathological and behavioral alterations similar to those observed in AD. Agmatine (Agm) has been shown to exert neuroprotective effects in central nervous system disorders. In this study, we investigated whether Agm treatment could attenuate apoptosis and improve cognitive decline in a STZ-induced Alzheimer rat model.

MATERIALS AND METHODS

We studied the effect of Agm on AD pathology using a STZ-induced Alzheimer rat model. For each experiment, rats were given anesthesia (chloral hydrate 300 mg/kg, ip), followed by a single injection of STZ (1.5 mg/kg) bilaterally into each lateral ventricle (5 μL/ventricle). Rats were injected with Agm (100 mg/kg) daily up to two weeks from the surgery day.

RESULTS

Agm suppressed the accumulation of amyloid beta and enhanced insulin signal transduction in STZ-induced Alzheimer rats [experimetal control (EC) group]. Upon evaluation of cognitive function by Morris water maze testing, significant improvement of learning and memory dysfunction in the STZ-Agm group was observed compared with the EC group. Western blot results revealed significant attenuation of the protein expressions of cleaved caspase-3 and Bax, as well as increases in the protein expressions of Bcl2, PI3K, Nrf2, and γ-glutamyl cysteine synthetase, in the STZ-Agm group.

CONCLUSION

Our results showed that Agm is involved in the activation of antioxidant signaling pathways and activation of insulin signal transduction. Accordingly, Agm may be a promising therapeutic agent for improving cognitive decline and attenuating apoptosis in AD.

Neuroprotective effect of ebselen against intracerebroventricular streptozotocin-induced neuronal apoptosis and oxidative stress in rats

The goal of this study was to examine the neuroprotective effect of ebselen against intracerebroventricular streptozotocin (ICV-STZ)-induced oxidative stress and neuronal apoptosis in rat brain. A total of 30 adult male Sprague-Dawley rats were randomly divided into 3 groups of 10 animals each: control, ICV-STZ, and ICV-STZ treated with ebselen. The ICV-STZ group rats were injected bilaterally with ICV-STZ (3 mg/kg) on days 1 and 3, and ebselen (10 mg/kg/day) was administered for 14 days starting from 1st day of ICV-STZ injection to day 14. Rats were killed at the end of the study and brain tissues were removed for biochemical and histopathological investigation. Our results demonstrated, for the first time, the neuroprotective effect of ebselen on Alzheimer's disease (AD) model in rats. Our present study, in ICV-STZ group, showed significant increase in tissue malondialdehyde levels and significant decrease in enzymatic antioxidants superoxide dismutase and glutathione peroxidase in the frontal cortex tissue. The histopathological studies in the brain of rats also supported that ebselen markedly reduced the ICV-STZ-induced histopathological changes and well preserved the normal histological architecture of the frontal cortex tissue. The number of apoptotic neurons was increased in frontal cortex tissue after ICV-STZ administration. Treatment of ebselen markedly reduced the number of degenerating apoptotic neurons. The study demonstrates the effectiveness of ebselen, as a powerful antioxidant, in preventing the oxidative damage and morphological changes caused by ICV-STZ in rats. Thus, ebselen may have a therapeutic value for the treatment of AD.

IGF-1-induced enhancement of PRNP expression depends on the negative regulation of transcription factor FOXO3a

The conformational conversion of the cellular prion protein (PrP^C) into its β-sheet-rich scrapie isoform (PrP^Sc) causes fatal prion diseases, which are also called transmissible spongiform encephalopathies (TSEs). Recent studies suggest that the expression of PrP^C by the PRNP gene is crucial for the development of TSEs. Therefore, the identification of the exogenous and endogenous stimulating factors that regulate PRNP expression would help to understand the pathogenesis of TSEs. Here, we demonstrate that forkhead box O3a (FOXO3a) negatively regulates PRNP expression by binding to the PRNP promoter, which is negatively regulated by insulin-like growth factor 1 (IGF-1). Our results show that the IGF-1-induced enhancement of PRNP mRNA and protein levels is due to the activation of the PI3K-Akt signaling pathway. The activation of Akt then induces the phosphorylation of FOXO3a, leading to its translocation from the nucleus to the cytoplasm and preventing its binding to the PRNP promoter. Treatment with the PI3K-Akt inhibitor LY294002 induces the nuclear retention of FOXO3a, which leads to a decrease in PRNP expression. We present a new IGF-1-PI3K-Akt-FOXO3a pathway, which influences PRNP expression. The results of this work are vital for understanding the function of PrP^C and for future therapeutic approaches to human TSEs.

Hydrogen sulfide in biochemistry and medicine

SIGNIFICANCE

An abundance of experimental evidence suggests that hydrogen sulfide (H(2)S) plays a prominent role in physiology and pathophysiology. Many targets exist for H(2)S therapy. The molecular targets of H(2)S include proteins, enzymes, transcription factors, and membrane ion channels.

RECENT ADVANCES

Novel H(2)S precursors are being synthesized and discovered that are capable of releasing H(2)S in a slow and sustained manner. This presents a novel and advantageous approach to H(2)S therapy for treatment of chronic conditions associated with a decline in endogenous H(2)S, such as diabetes and cardiovascular disease.

CRITICAL ISSUES

While H(2)S is cytoprotective at physiological concentrations, it is not universally cytoprotective, as it appears to have pro-apoptotic actions in cancer cells and is well known to be toxic at supraphysiological concentrations. Many of the pleiotropic effects of H(2)S on health are associated with the inhibition of inflammation and upregulation of prosurvival pathways. The powerful anti-inflammatory, cytoprotective, immunomodulating, and trophic effects of H(2)S on the vast majority of normal cells seem to be mediated mainly by its actions as an extremely versatile direct and indirect antioxidant and free radical scavenger. While the overall effects of H(2)S on transformed (i.e., malignant) cells can be characterized as pro-oxidant and pro-apoptotic, they contrast sharply with the cytoprotective effects on most normal cells.

FUTURE DIRECTIONS

H(2)S has become a molecule of great interest, and several slow-releasing H(2)S prodrugs are currently under development. We believe that additional agents regulating H(2)S bioavailability will be developed during the next 10 years.

Involvement of the up-regulated FoxO1 expression in follicular granulosa cell apoptosis induced by oxidative stress

Follicular atresia is common in female mammalian ovaries, where most follicles undergo degeneration at any stage of growth and development. Oxidative stress gives rise to triggering granulosa cell apoptosis, which has been suggested as a major cause of follicular atresia. However, the underlying mechanism by which the oxidative stress induces follicular atresia remains unclear. FoxO transcription factors are known as critical mediators in the regulation of oxidative stress and apoptosis. In this study, the involvement of FoxO1 in oxidative stress-induced apoptosis of mouse follicular granulosa cells (MGCs) was investigated in vivo and in vitro. It was observed that increased apoptotic signals correlated with elevated expression of FoxO1 in MGCs when mice were treated with the oxidant. Correspondingly, the expressions of FoxO1 target genes, such as proapoptotic genes and antioxidative genes, were also up-regulated. In primary cultured MGCs, treatment with H(2)O(2) led to FoxO1 nuclear translocation. Further studies with overexpression and knockdown of FoxO1 demonstrated the critical role of FoxO1 in the induction of MGC apoptosis by oxidative stress. Finally, inactivation of FoxO1 by insulin treatment confirmed that FoxO1 induced by oxidative stress played a pivotal role in up-regulating the expression of downstream apoptosis-related genes in MGCs. Our results suggest that up-regulation of FoxO1 by oxidative stress leads to apoptosis of granulosa cells, which eventually results in follicular atresia in mice.

Redox-regulating role of insulin: the essence of insulin effect

It is well-known that insulin acts as an important hormone, controlling energy metabolism, cellular proliferation and biosynthesis of functional molecules to maintain a biological homeostasis. Over the past few years, intensive insulin therapy has been believed to be benefit for the outcome of diabetic patients, in which the suppression of oxidative stress plays a role. Moreover, insulin is accepted as a key component of glucose-insulin-potassium, a treatment which has been believed to exert significant cardiovascular protective effect via the reduction of oxidative stress. Furthermore, accumulating evidence has suggested that insulin exerts important redox-regulating actions in various insulin-sensitive target organs, implying the systematic antioxidative role of insulin as a hormone. It is time for us to revisit insulin effects, through summarizing and evaluating the novel functions of insulin and their mechanisms. This review focuses on the antioxidative effect of insulin and highlights insulin-induced regulation of various antioxidant enzymes via insulin signaling pathways and the cross talk between key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor κB (NF-κB) which are responsible for the transcription of antioxidant enzymes, leading to reduced generation of reactive oxygen species (ROS) and the enhancement of the elimination of ROS.

Morphological and biochemical studies on aging and autophagy

To maintain health in the elderly is a crucial objective for modern medicine that involves both basic and clinical researches. Autophagy is a fundamental auto-cannibalizing process that preserves cellular homeostasis and, if altered, either by excess or defect, greatly changes cell fate and can result in incapacitating human diseases. Efficient autophagy may prolong lifespan, but unfortunately this process becomes less efficient with age. The present review is focused on the close relationship between autophagy and age-related disorders in different tissues/organs and in transgenic animal models. In particular, it comments on the up to date literature on mechanisms responsible for age-related impairment of autophagy. Moreover, before discussing about these mechanisms, it is necessary to describe the metabolic autophagic regulation of autophagy and the proteins involved in this process. At the end, these data would summarize the autophagic link with aging process, as important tools in the future biogerontology scenario.

Theories and mechanisms of aging

This article discusses various theories of aging and their relative plausibility related to the human aging process. Structural and physiologic changes of aging are discussed in detail by organ system. Each of the organ systems is discussed when applicable to the various theories of aging. Normal versus abnormal aging is discussed in the context of specific aging processes, with atypical presentations of disease and general links to life expectancy. Life expectancy and lifespan are discussed in the context of advances in medical science and the potential ultimate link to human life span.

Redox pioneer: Professor Wulf Dröge

Dr. Wulf Dröge is recognized here as a redox pioneer because he has published as first author an article on antioxidant/redox biology that has been cited more than 2000 times and over 10 articles that have been cited more than 100 times. One of the key discoveries (1987) was the stimulatory effect of superoxide radicals and hydrogen peroxide on lymphocyte functions, which triggered a series of studies on the role of reactive oxygen species, glutathione, and its precursor cysteine in physiological and pathological processes. He discovered abnormally low cysteine and glutathione levels in human immunodeficiency virus-infected patients and the age-related decline in the postabsorptive plasma cysteine concentration, which is believed to cause age-related oxidative stress. He developed a theoretical concept of the mechanism of aging and death, which is outlined in his books Avoiding the First Cause of Death and Challenging the Limits of the Human Lifespan.

Insulin-resistant brain state: the culprit in sporadic Alzheimer's disease?

Severe abnormalities in brain glucose/energy metabolism and insulin signaling have been documented to take a pivotal role in early sporadic Alzheimer's disease (sAD) pathology. Indeed, the "insulin-resistant brain state" has been hypothesized to form the core of the neurodegenerative events that occur in sAD. In this vein, intracerebroventricular administration of subdiabetogenic doses of streptozotocin (STZ) in rats can induce an insulin-resistant brain state, which is proposed as a suitable experimental model of sAD. This review highlights the involvement of disturbed brain insulin metabolism in sAD etiopathogenesis. Furthermore, current knowledge demonstrates that central STZ administration produces brain pathology and behavioral changes that resemble changes found in sAD patients. The STZ-intracerebroventricularly treated rat represents a promising experimental tool in this field by providing new insights concerning early brain alterations in sAD, which can be translated in novel etiopathogenic and therapeutic approaches in this disease.

Cysteine/cystine redox signaling in cardiovascular disease

Extracellular thiol/disulfide redox environments are highly regulated in healthy individuals. The major thiol/disulfide redox couple in human plasma is cysteine (Cys) and its disulfide form, cystine (CySS). Oxidation of this redox couple, measured as a more positive steady-state redox potential (E(h)), is associated with risk factors for cardiovascular disease (CVD), including aging, smoking, obesity, and alcohol abuse. Rodent and vascular cell studies show that the extracellular redox state of Cys/CySS (E(h)CySS) can play a vital role in controlling CVD through proinflammatory signaling. This inflammatory signaling is regulated by cell-surface protein redox state and involves mitochondrial oxidation, nuclear factor-κB activation, and elevated expression of genes for monocyte recruitment to endothelial cells. Gene array and proteomics studies reveal the global nature of redox effects, and different cell types, e.g., endothelial cells, monocytes, fibroblasts, and epithelial cells, show cell-specific redox responses with different phenotypic traits, e.g., proliferation and apoptosis, which can contribute to CVD. The critical nature of the proinflammatory redox signaling and cell biology associated with E(h)CySS supports the use of plasma levels of Cys, CySS, and E(h)CySS as key indicators of vascular health. Plasma redox-state-based pharmacologic interventions to control or improve E(h)CySS may be effective in preventing CVD onset or progression.

Forkhead homeobox type O transcription factors in the responses to oxidative stress

Reactive oxygen species (ROS) and cellular oxidative stress are involved in many physiological and pathophysiological processes, including cellular and organismal aging, migration, proliferation, senescence or death of normal and cancer cells, and stress resistance of stem cells. The forkhead homeobox type O (FOXO) transcription factors FOXO1, FOXO3a, and FOXO4 are critical mediators of the cellular responses to oxidative stress and have been implicated in many of the above ROS-regulated processes. In cancer cells they converge oxidative stress signaling to cell cycle arrest and cell death or promote a motile phenotype. Dependent on their posttranslational modifications FOXOs can also actively regulate the detoxification of cells from ROS and promote stress resistance. Thus, FOXO transcription factors are of vital importance in processes regulating tumor survival or progression, stem cell maintenance, age-related pathological processes, and lifespan extension.

Autophagy and aging: lessons from progeria models

Autophagy is an evolutionarily conserved process essential for cellular homeostasis and organismal viability. In fact, this pathway is one of the major protein degradation mechanisms in eukaryotic cells. It has been repeatedly reported that the autophagic activity of living cells decreases with age, probably contributing to the accumulation of damaged macromolecules and organelles during aging. Moreover, autophagy modulation in different model organisms has yielded very promising results suggesting that the maintenance of a proper autophagic activity contributes to extend longevity. On the other hand, recent findings have shown that distinct premature-aging murine models exhibit an extensive basal activation of autophagy instead of the characteristic decline in this process occurring during normal aging. This unexpected autophagic increase in progeroid models is usually associated with a series of metabolic alterations resembling those occurring under calorie restriction or in other situations reported to prolong life-span. In this chapter, we will discuss the current knowledge on the relationship between the autophagy pathway and aging with a special emphasis on the unexpected and novel link between premature aging and autophagy up-regulation.

Hepatic autophagy is suppressed in the presence of insulin resistance and hyperinsulinemia: inhibition of FoxO1-dependent expression of key autophagy genes by insulin

Autophagy is essential for maintaining both survival and health of cells. Autophagy is normally suppressed by amino acids and insulin. It is unclear what happens to the autophagy activity in the presence of insulin resistance and hyperinsulinemia. In this study, we examined the autophagy activity in the presence of insulin resistance and hyperinsulinemia and the associated mechanism. Insulin resistance and hyperinsulinemia were induced in mice by a high fat diet, followed by measurements of autophagy markers. Our results show that autophagy was suppressed in the livers of mice with insulin resistance and hyperinsulinemia. Transcript levels of some key autophagy genes were also suppressed in the presence of insulin resistance and hyperinsulinemia. Conversely, autophagy activity was increased in the livers of mice with streptozotocin-induced insulin deficiency. Levels of vps34, atg12, and gabarapl1 transcripts were elevated in the livers of mice with insulin deficiency. To study the mechanism, autophagy was induced by nutrient deprivation or glucagon in cultured hepatocytes in the presence or absence of insulin. Autophagy activity and transcript levels of vps34, atg12, and gabarapl1 genes were reduced by insulin. The effect of insulin was largely prevented by overexpression of the constitutive nuclear form of FoxO1. Importantly, autophagy of mitochondria (mitophagy) in cultured cells was suppressed by insulin in the presence of insulin resistance. Together, our results show that autophagy activity and expression of some key autophagy genes were suppressed in the presence of insulin resistance and hyperinsulinemia. Insulin suppression of autophagy involves FoxO1-mediated transcription of key autophagy genes.

Increased age reduces DAF-16 and SKN-1 signaling and the hormetic response of Caenorhabditis elegans to the xenobiotic juglone

Cells adapt to stressors by activating mechanisms that repair damage and protect them from further injury. Stress-induced damage accumulates with age and contributes to age associated diseases. Increased age attenuates the ability to mount a stress response, but little is known about the mechanisms by which this occurs. To begin addressing this problem, we studied hormesis in the nematode Caenorhabditis elegans. When exposed to a low concentration of the xenobiotic juglone, young worms mount a robust hormetic stress response and survive a subsequent exposure to a higher concentration of juglone that is normally lethal to naïve animals. Old worms are unable to mount this adaptive response. Microarray and RNAi analyses demonstrate that an altered transcriptional response to juglone is responsible in part for the reduced adaptation of old worms. Many genes differentially regulated in young versus old animals are known or postulated to be regulated by the FOXO homologue DAF-16 and the Nrf2 homologue SKN-1. Activation of these pathways is greatly reduced in juglone stressed old worms. DAF-16- and SKN-1-like transcription factors play highly conserved roles in regulating stress resistance and longevity genes. Our studies provide a foundation for developing a molecular understanding of how age affects cytoprotective transcriptional pathways.

Homeostatic functions of the p53 tumor suppressor: regulation of energy metabolism and antioxidant defense

The p53 tumor suppressor plays pivotal role in the organism by supervising strict compliance of individual cells to needs of the whole organisms. It has been widely accepted that p53 acts in response to stresses and abnormalities in cell physiology by mobilizing the repair processes or by removing the diseased cells through initiating the cell death programs. Recent studies, however, indicate that even under normal physiological conditions certain activities of p53 participate in homeostatic regulation of metabolic processes and that these activities are important for prevention of cancer. These novel functions of p53 help to align metabolic processes with the proliferation and energy status, to maintain optimal mode of glucose metabolism and to boost the energy efficient mitochondrial respiration in response to ATP deficiency. Additional activities of p53 in non-stressed cells tune up the antioxidant defense mechanisms reducing the probability of mutations caused by DNA oxidation under conditions of daily stresses. The deficiency in the p53-mediated regulation of glycolysis and mitochondrial respiration greatly accounts for the deficient respiration of the predominance of aerobic glycolysis in cancer cells (the Warburg effect), while the deficiency in the p53-modulated antioxidant defense mechanisms contributes to mutagenesis and additionally boosts the carcinogenesis process.

Autophagy and aging: keeping that old broom working

Autophagy, a highly conserved mechanism of quality control inside cells, is essential for the maintenance of cellular homeostasis and for the orchestration of an efficient cellular response to stress. The decrease in autophagic activity observed in almost all cells and tissues as organisms age was proposed to contribute to different aspects of the aging phenotype and to the aggravation of detrimental age-related diseases. The recent advances in our understanding of the molecular mechanisms underlying autophagy and the identification of the subset of genes involved in this process has enabled the use of genetic manipulations to start testing this hypothesis. Here, I review the recent genetic evidence in support of tight connections between autophagy, health span and aging.