Protective effect of S-allyl-L-cysteine, a garlic compound, on amyloid beta-protein-induced cell death in nerve growth factor-differentiated PC12 cells

Elephant Black Garlic's Beneficial Properties for Hippocampal Neuronal Network, Chemical Characterization and Biological Evaluation

Garlic has been used for decades as an important food and additionally for its beneficial properties in terms of nutrition and ancestral therapeutics. In this work, we compare the properties of fresh (WG) and aged (BG) extract obtained from elephant garlic, harvested on Chiloe Island, Chile. BG was prepared from WG with a 20-day aging process under controlled temperature and humidity conditions. We observed that in BG, compounds such as diallyl disulfide decrease, and compounds of interest such as 5-hydroxymethylfurfural (69%), diallyl sulfide (17%), 3H-1,2-Dithiole (22%) and 4-Methyl-1,2,3-trithiolane (16%) were shown to be increased. Using 2,2-diphenyl-1-picrylhydrazyl (DPPH, BG: 51 ± 5.7%, WG: 12 ± 2.6%) and 2,20-azino-bis-(3-ethylbenzothiazoline-6 sulfonate) diammonium salt (ABTS, BG: 69.4 ± 2.3%, WG: 21 ± 3.9%) assays, we observed that BG possesses significantly higher antioxidant activity than WG and increased cell viability in hippocampal slices (41 ± 9%). The effects of WG and BG were shown to improve the neuronal function through an increased in intracellular calcium transients (189 ± 4%). In parallel, BG induced an increase in synaptic vesicle protein 2 (SV-2; 75 ± 12%) and brain-derived neurotrophic factor (BDNF; 32 ± 12%) levels. Thus, our study provides the initial scientific bases to foster the use of BG from Chiloe Island as a functional food containing a mixture of bioactive compounds that may contribute to brain health and well-being.

Immunomodulatory effects of Allium Sativum L. and its constituents against viral infections and metabolic diseases

BACKGROUND

Allium sativum L., or garlic, is one of the most studied plants worldwide within the field of traditional medicine. Current interests lie in the potential use of garlic as a preventive measure and adjuvant treatment for viral infections, e.g., SARS-CoV-2. Even though it cannot be presented as a single treatment, its beneficial effects are beyond doubt. The World Health Organization has deemed it an essential part of any balanced diet with immunomodulatory properties.

OBJECTIVE

The aim of the study was to review the literature on the effects of garlic compounds and preparations on immunomodulation and viral infection management, with emphasis on SARS-CoV-2.

METHOD

Exhaustive literature search has been carried out on electronic databases.

CONCLUSION

Garlic is a fundamental part of a well-balanced diet which helps maintain general good health. The reported information regarding garlic's ability to beneficially modulate inflammation and the immune system is encouraging. Nonetheless, more efforts must be made to understand the actual medicinal properties and mechanisms of action of the compounds found in this plant to inhibit or diminish viral infections, particularly SARS-CoV-2. Based on our findings, we propose a series of innovative strategies to achieve such a challenge in the near future.

Therapeutic Effects of Natural Compounds and Small Molecule Inhibitors Targeting Endoplasmic Reticulum Stress in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disease, characterized by progressive cognitive impairment and memory loss. So far, the pathogenesis of AD has not been fully understood. Research have shown that endoplasmic reticulum (ER) stress and unfolded protein response (UPR) participate in the occurrence and development of AD. Furthermore, various studies, both in vivo and in vitro, have shown that targeting ER stress and ER stress-mediated apoptosis contribute to the recovery of AD. Thus, targeting ER stress and ER stress-mediated apoptosis may be effective for treating AD. In this review, the molecular mechanism of ER stress and ER stress-mediated apoptosis, as well as the therapeutic effects of some natural compounds and small molecule inhibitors targeting ER stress and ER stress-mediated apoptosis in AD will be introduced.

S-allyl cysteine ameliorates heat stress-induced oxidative stress by activating Nrf2/HO-1 signaling pathway in BMECs

Heat stress-induced oxidative stress in bovine mammary epithelial cells (BMECs) threatens the normal growth and development of bovine mammary tissue, resulting in lower milk production of dairy cows. The aim of the present study is to investigate the protective effects of S-allyl cysteine (SAC), an organosulfur component extracted from aged garlic, on heat stress-induced oxidative stress and apoptosis in BMECs and to explore its underlying mechanisms. Our results showed that heat stress treatment considerably decreased cell viability, whereas SAC treatment dose-dependently restored cell viability of BMECs under heat-stress conditions. In addition, SAC protected BMECs from heat stress-induced oxidative damage by inhibiting the excessive accumulation of reactive oxygen species (ROS) and increasing the activity of antioxidant enzymes. It also inhibited heat stress-induced apoptosis by reducing the ratio of Bax/Bcl-2 and blocking proteolytic the cleavage of caspase-3 in BMECs. Interestingly, we found that the protective effect of SAC on heat stress-induced oxidative stress and apoptosis was dependent on the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway. SAC promoted the Nrf2 nuclear translocation in heat stress-induced BMECs. The results were also validated by Nrf2 and Keap1 knockdown experiments further demonstrating that Nrf-2 was indeed involved in the protective effect of SAC on heat stress-induced oxidative damage and apoptosis. In summary, our results showed that SAC could protect BMECs from heat stress-induced injury by mediating the Nrf2/HO-1 signaling pathway, suggesting that SAC could be considered as a therapeutic drug for attenuating heat stress-induced mammary gland diseases.

Attenuation of Nrf2/Keap1/ARE in Alzheimer's Disease by Plant Secondary Metabolites: A Mechanistic Review

Alzheimer’s disease (AD) is a progressive neuronal/cognitional dysfunction, leading to disability and death. Despite advances in revealing the pathophysiological mechanisms behind AD, no effective treatment has yet been provided. It urges the need for finding novel multi-target agents in combating the complex dysregulated mechanisms in AD. Amongst the dysregulated pathophysiological pathways in AD, oxidative stress seems to play a critical role in the pathogenesis progression of AD, with a dominant role of nuclear factor erythroid 2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein-1 (Keap1)/antioxidant responsive elements (ARE) pathway. In the present study, a comprehensive review was conducted using the existing electronic databases, including PubMed, Medline, Web of Science, and Scopus, as well as related articles in the field. Nrf2/Keap1/ARE has shown to be the upstream orchestrate of oxidative pathways, which also ameliorates various inflammatory and apoptotic pathways. So, developing multi-target agents with higher efficacy and lower side effects could pave the road in the prevention/management of AD. The plant kingdom is now a great source of natural secondary metabolites in targeting Nrf2/Keap1/ARE. Among natural entities, phenolic compounds, alkaloids, terpene/terpenoids, carotenoids, sulfur-compounds, as well as some other miscellaneous plant-derived compounds have shown promising future accordingly. Prevailing evidence has shown that activating Nrf2/ARE and downstream antioxidant enzymes, as well as inhibiting Keap1 could play hopeful roles in overcoming AD. The current review highlights the neuroprotective effects of plant secondary metabolites through targeting Nrf2/Keap1/ARE and downstream interconnected mediators in combating AD.

Sulfur-containing Secondary Metabolites as Neuroprotective Agents

Sulfur-containing secondary metabolites are a relatively small group of substances of plant origin. The present review is focused on their neuroprotective properties. The results obtained in a series of in vitro and in vivo studies are reported. Among glucosinolates, the wide class of compounds in the sulfur-containing metabolites, glucoraphanin, sulforaphane and isothiocyanates proved to be the more studied in this context and showed interesting properties as modulators of several systems involved in the pathogenesis of neurologic diseases such as oxidative stress, inflammation and apoptosis. Allium sativum L. (garlic) is widely known for its sulfur-containing components endowed with health-promoting activities and its medicinal properties are known from ancient times. In recent studies, garlic components proved active in neuroprotection due to the direct and indirect antioxidant properties, modulation of apoptosis mediators and inhibiting the formation of amyloid protein. Dihydroasparagusic acid, the first dimercaptanic compound isolated from a natural source, effectively inhibited inflammatory and oxidative processes that are important factors for the etiopathogenesis of neurodegenerative diseases, not only for its antioxidant and radical scavenging properties but also because it may down-regulate the expression of several microglial-derived inflammatory mediators. Serofendic acid represents a rare case of sulfur-containing animal-derived secondary metabolite isolated from fetal calf serum extract. It proved effective in the suppression of ROS generation and in the expression of several inflammatory and apoptosis mediators and showed a cytotrophic property in astrocytes, promoting the stellation process. Lastly, the properties of hydrogen sulfide were also reported since in recent times it has been recognized as a signaling molecule and as a mediator in regulating neuron death or survival. It may be produced endogenously from cysteine but may also be released by sulfur-containing secondary metabolites, mainly from those present in garlic.

Neuroprotective mechanisms of S-allyl-L-cysteine in neurological disease

S-allyl-L-cysteine (SAC) is a sulfur-containing amino acid present in garlic and exhibits a wide range of biological activities such as antioxidant, anti-inflammatory, and anticancer agent. An earlier study demonstrated that SAC ameliorates oxidative damage in a model of experimental stroke. However, the antioxidant property of SAC does not suffice to explain its beneficial effects in terms of the underlying mechanisms. Endoplasmic reticulum (ER) stress and ER stress-induced cell death have been shown to be involved in various neurological diseases such as brain ischemia, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease. We have previously demonstrated that SAC exerts significant protective effects against ER stress-induced neurotoxicity in cultured rat hippocampal neurons and organotypic hippocampal slice cultures. Recently, we demonstrated that these results are due to the direct suppression of calpain activity via the binding of SAC to this enzyme's Ca²⁺-binding domain. We also found that the protective effects of the side-chain-modified SAC derivatives, S-ethyl-L-cysteine (SEC) and S-propyl-L-cysteine (SPC), against ER stress-induced neurotoxicity were more potent than those of SAC in cultured rat hippocampal neurons. In addition, SAC, SEC and SPC have been shown to decrease the production of amyloid-β peptide in the brains of mice with D-galactose-induced aging. These three hydrophilic cysteine-containing compounds have also been shown to exert neuroprotective effects against dopaminergic neuron injury in a murine model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In this review, we aim to provide a current overview of the protective actions of SAC and the SAC-related compounds, SEC and SPC, in neurodegenerative disease and discuss the promise of SAC as a prototype for developing novel therapeutic drugs for neurological diseases.

Canola Oil as an Economical Lipid Source in Gel Larval Diet for Queensland Fruit Fly

A new sterile insect technique (SIT) program is currently being developed for management of the Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), the most costly challenge to Australian horticulture in the eastern states. SIT relies on cost-effective mass production of millions of high-quality flies. A recently developed gel larval diet has proven effective, enabling production of large numbers of high-quality flies, but includes some costly ingredients. With a basic diet now available, current research focuses on refining the formulation to deliver a more economical diet. Wheat germ oil (WGO) is the main lipid source in the current Queensland fruit fly gel diet, but is a particularly expensive ingredient and has limited availability. To identify an oil that maintains high productivity and fly quality at reduced cost, the present study assessed production and performance of Queensland fruit flies reared on gel larval diets containing the WGO that was used in previous studies (WGO/M), an alternative WGO (WGO/A), sunflower oil, rice bran oil, and canola oil. Diets containing canola oil ($5.24/liter) performed as well as diets with WGO/M ($116/liter) in terms of parental egg hatch, pupal number, pupal weight, adult emergence, percentage and rate of fliers, sex ratio, fecundity, and fertility (F1 egg hatch), offering a remarkably cost-effective alternative. Costs of oil in Queensland fruit fly production are reduced by ca. 95% per 1,000 flight capable adults ('fliers'). Substantial savings may be made in Queensland fruit fly mass rearing by substituting WGO/M with canola oil in gel larval diets without compromising productivity.

Neuroprotective Effects of Aged Garlic Extract on Cognitive Dysfunction and Neuroinflammation Induced by β-Amyloid in Rats

Neuroinflammation is pathological evidence of Alzheimer's disease (AD) that likely starts as a host defense response to the damaging effects of the β-amyloid (Aβ) deposits in the brain. The activation of microglia may promote the neurodegenerative process through the release of proinflammatory cytokines, such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα), which may lead to neuronal damage and eventual death. Aged garlic extract (AGE) has been reported to have multiple biological activities, including anti-inflammatory effects. Therefore, the objective of this study was to investigate the effect of AGE on Aβ (1-42)-induced cognitive dysfunction and neuroinflammation. Adult male Wistar rats were given AGE (125, 250, and 500 mg/kg BW, body weight), orally administered, daily for 56 days. They were then injected with 1 μL of aggregated Aβ (1-42) into the lateral ventricles; bilaterally. Seven days later, their recognition memory was evaluated using a novel object recognition (NOR) test. Then the rats were sacrificed to investigate the alteration of microglia cells, IL-1β and TNFα in the cerebral cortex and hippocampus. The results indicated that AGE at doses of 250 and 500 mg/kg BW significantly improved short-term recognition memory in cognitively impaired rats. In addition, AGE significantly minimized the inflammatory response by reducing the activation of microglia and IL-1β to the levels found in the control, which is similar to the results found in Celebrex-treated rats. In conclusion, AGE may be useful for improving the short-term recognition memory and relieve the neuroinflammation in Aβ-induced rats.

Essential oils from two Allium species exert effects on cell proliferation and neuroblast differentiation in the mouse dentate gyrus by modulating brain-derived neurotrophic factor and acetylcholinesterase

Background

In the present study, we investigated the effects of oil products from two Allium species: Allium sativum (garlic) and Allium hookeri (Chinese chives) on cell proliferation and neuroblast differentiation in the mouse dentate gyrus.

Methods

Using corn oil as a vehicle, the essential oil from garlic (10 ml/kg), or Chinese chives (10 ml/kg) was administered orally to 9-week-old mice once a day for 3 weeks. One hour following the last treatment, a novel object recognition test was conducted and the animals were killed 2 h after the test.

Results

In comparison to the vehicle-treated group, garlic essential oil (GO) treatment resulted in significantly increased exploration time and discrimination index during the novel object recognition test, while Chinese chives essential oil (CO) reduced the exploration time and discrimination index in the same test. In addition, the number of Ki67-immunoreactive proliferating cells and doublecortin-immunoreactive neuroblasts significantly increased in the dentate gyrus of GO-treated animals. However, administration of CO significantly decreased cell proliferation and neuroblast differentiation. Administration of GO significantly increased brain-derived neurotrophic factor (BDNF) levels and decreased acetylcholinesterase (AChE) activity in the hippocampal homogenates. In contrast, administration of CO decreased BDNF protein levels and had no significant effect on AChE activity, compared to that in the vehicle-treated group.

Conclusions

These results suggest that GO significantly improves novel object recognition as well as increases cell proliferation and neuroblast differentiation, by modulating hippocampal BDNF protein levels and AChE activity, while CO impairs novel object recognition and decreases cell proliferation and neuroblast differentiation, by reducing BDNF protein levels in the hippocampus.

Screening of dietary antioxidants against mitochondria-mediated oxidative stress by visualization of intracellular redox state

Mitochondrial impairment and the resulting generation of reactive oxygen species (ROS) have been associated with aging and its related pathological conditions. Recently, dietary antioxidants have gained significant attention as potential preventive and therapeutic agents against ROS-generated aging and pathological conditions. We previously demonstrated that food-derived antioxidants prevented intracellular oxidative stress under proteasome inhibition conditions, which was attributed to mitochondrial dysfunction and ROS generation, followed by cell death. Here, we further screened dietary antioxidants for their activity as redox modulators by visualization of the redox state using Redoxfluor, a fluorescent protein redox probe. Direct alleviation of ROS by antioxidants, but not induction of antioxidative enzymes, prevented mitochondria-mediated intracellular oxidation. The effective antioxidants scavenged mitochondrial ROS and suppressed cell death. Our study indicates that redox visualization under mitochondria-mediated oxidative stress is useful for screening potential antioxidants to counteract mitochondrial dysfunction, which has been implicated in aging and the pathogenesis of aging-related diseases.

4-Hydroxy-nonenal-A Bioactive Lipid Peroxidation Product

This review on recent research advances of the lipid peroxidation product 4-hydroxy-nonenal (HNE) has four major topics: I. the formation of HNE in various organs and tissues, II. the diverse biochemical reactions with Michael adduct formation as the most prominent one, III. the endogenous targets of HNE, primarily peptides and proteins (here the mechanisms of covalent adduct formation are described and the (patho-) physiological consequences discussed), and IV. the metabolism of HNE leading to a great number of degradation products, some of which are excreted in urine and may serve as non-invasive biomarkers of oxidative stress.

Differential modulation of apoptotic processes by proanthocyanidins as a dietary strategy for delaying chronic pathologies

Apoptosis is a biological process necessary for maintaining cellular homeostasis. Several diseases can result if it is deregulated. For example, inhibition of apoptotic signaling pathways is linked to the survival of pathological cells, which contributes to cancer, whereas excessive apoptosis is linked to neurodegenerative diseases, partially via oxidative stress. The activation or restoration of apoptosis via extrinsic or intrinsic pathways combined with cell signaling pathways triggered by reactive oxygen specises (ROS) formation is considered a key strategy by which bioactive foods can exert their health effects. Proanthocyanidins, a class of flavonoids naturally found in fruits, vegetables, and beverages, have attracted a great deal of attention not only because they are strong antioxidants but also because they appear to exert a different modulation of apoptosis, stimulating apoptosis in damaged cells, thus preventing cancer or reducing apoptosis in healthy cells, and as a result, preserving the integrity of normal cells and protecting against neurodegenerative diseases. Therefore, proanthocyanidins could provide a defense against apoptosis induced by oxidative stress or directly inhibit apoptosis, and they could also provide a promising treatment for a variety of diseases. Emerging data suggest that proanthocyanidins, especially those that humans can be persuaded to consume, may be used to prevent and manage cancer and mental disorders.

Protective effect of S-allyl-L-cysteine against endoplasmic reticulum stress-induced neuronal death is mediated by inhibition of calpain

Endoplasmic reticulum (ER) stress, implicated in various neurodegenerative processes, increases the level of intracellular Ca(2+) and leads to activation of calpain, a Ca(2+)-dependent cysteine protease. We have shown previously that S-allyl-L-cysteine (SAC) in aged garlic extracts significantly protects cultured rat hippocampal neurons (HPNs) against ER stress-induced neurotoxicity. The neuroprotective effect of SAC was compared with those of the related antioxidant compounds, L-cysteine (CYS) and N-acetylcysteine (NAC), on calpain activity in HPNs and also in vitro. SAC, but not CYS or NAC, reversibly restored the survival of HPNs and increased the degradation of α-spectrin, a substrate for calpain, induced by tunicamycin, a typical ER stress inducer. Activities of μ- and m-calpains in vitro were also concentration dependently suppressed by SAC, but not by CYS or NAC. At submaximal concentration, although ALLN (5 pM), which blocks the active site of calpain, and calpastatin (100 pM), an endogenous calpain-inhibitor protein, additively inhibited μ-calpain activity in vitro in combination with SAC, the effect of PD150606 (25 μM), which prevents interaction of Ca(2+) with the Ca(2+)-binding site of calpain, was unaffected by SAC. In contrast, SAC (1 mM) significantly reversed the effect of PD150606 at a concentration that elicited supramaximal inhibition (100 μM), but did not affect ALLN (1 nM)- and calpastatin (100 nM)-induced inhibition of μ-calpain activity. These results suggest that the protective effects of SAC against ER stress-induced neuronal cell death are not attributable to antioxidant activity, but to suppression of calpain through interaction with its Ca(2+)-binding site.

Ameliorating effects of aged garlic extracts against Aβ-induced neurotoxicity and cognitive impairment

Background

In vitro antioxidant activities and neuron-like PC12 cell protective effects of solvent fractions from aged garlic extracts were investigated to evaluate their anti-amnesic functions. Ethyl acetate fractions of aged garlic had higher total phenolics than other fractions.

Methods

Antioxidant activities of ethyl acetate fractions from aged garlic were examined using 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) and malondialdehyde (MDA) inhibitory effect using mouse whole brain homogenates. Levels of cellular oxidative stress as reactive oxygen species (ROS) accumulation were measured using 2',7'-dichlorofluorescein diacetate (DCF-DA). PC12 cell viability was investigated by 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and lactate dehydtrogenase (LDH) assay. The learning and memory impairment in institute of cancer research (ICR) mice was induced by neurotoxic amyloid beta protein (Aβ) to investigate in vivo anti-amnesic effects of aged garlic extracts by using Y-maze and passive avoidance tests.

Results

We discovered that ethyl acetate fractions showed the highest ABTS radical scavenging activity and MDA inhibitory effect. Intracellular ROS accumulation resulting from Aβ treatment in PC12 cells was significantly reduced when ethyl acetate fractions were presented in the medium compare to PC12 cells which was only treated with Aβ only. Ethyl acetate fractions from aged garlic extracts showed protection against Aβ-induced neurotoxicity. Pre-administration with aged garlic extracts attenuated Aβ-induced learning and memory deficits in both in vivo tests.

Conclusions

Our findings suggest that aged garlic extracts with antioxidant activities may improve cognitive impairment against Aβ-induced neuronal deficit, and possess a wide range of beneficial activities for neurodegenerative disorders, notably Alzheimer's disease (AD).

The antioxidant mechanisms underlying the aged garlic extract- and S-allylcysteine-induced protection

Aged garlic extract (AGE) is an odorless garlic preparation containing S-allylcysteine (SAC) as its most abundant compound. A large number of studies have demonstrated the antioxidant activity of AGE and SAC in both in vivo--in diverse experimental animal models associated to oxidative stress--and in vitro conditions--using several methods to scavenge reactive oxygen species or to induce oxidative damage. Derived from these experiments, the protective effects of AGE and SAC have been associated with the prevention or amelioration of oxidative stress. In this work, we reviewed different antioxidant mechanisms (scavenging of free radicals and prooxidant species, induction of antioxidant enzymes, activation of Nrf2 factor, inhibition of prooxidant enzymes, and chelating effects) involved in the protective actions of AGE and SAC, thereby emphasizing their potential use as therapeutic agents. In addition, we highlight the ability of SAC to activate Nrf2 factor--a master regulator of the cellular redox state. Here, we include original data showing the ability of SAC to activate Nrf2 factor in cerebral cortex. Therefore, we conclude that the therapeutic properties of these molecules comprise cellular and molecular mechanisms at different levels.

Neuroprotective effect of honokiol and magnolol, compounds from Magnolia officinalis, on beta-amyloid-induced toxicity in PC12 cells

Amyloid β peptide (Aβ) induced toxicity is a well-established pathway of neuronal cell death which might play a role in Alzheimer's disease. In this regard, the toxic effect of Aβ on a cultured Aβ-sensitive neuronal cell line was used as a primary screening tool for potential anti-Alzheimer's therapeutic agents. The effects of nine pure compounds (vitamin E, α-asarone, salidroside, baicolin, magnolol, gastrodin, bilobalide, honokiol and β-asarone) from selected Chinese herbs on neuronal cell death induced by Aβ in NGF-differentiated PC12 cells were examined. Only two of the studied compounds, honokiol and magnolol, significantly decreased Aβ-induced cell death. Further experiments indicated that their neuroprotective effects are possibly mediated through reduced ROS production as well as suppression of intracellular calcium elevation and inhibition of caspase-3 activity. The results provide for the first time a scientific rationale for the clinical use of honokiol and magnolol in the treatment of Alzheimer's disease.

Chemistry and biochemistry of lipid peroxidation products

Oxidative stress and resulting lipid peroxidation is involved in various and numerous pathological states including inflammation, atherosclerosis, neurodegenerative diseases and cancer. This review is focused on recent advances concerning the formation, metabolism and reactivity towards macromolecules of lipid peroxidation breakdown products, some of which being considered as 'second messengers' of oxidative stress. This review relates also new advances regarding apoptosis induction, survival/proliferation processes and autophagy regulated by 4-hydroxynonenal, a major product of omega-6 fatty acid peroxidation, in relationship with detoxication mechanisms. The use of these lipid peroxidation products as oxidative stress/lipid peroxidation biomarkers is also addressed.

Cocoa procyanidins attenuate 4-hydroxynonenal-induced apoptosis of PC12 cells by directly inhibiting mitogen-activated protein kinase kinase 4 activity

Neurodegenerative disorders such as Alzheimer's disease (AD) are associated with oxidative stress, and it has been suggested that apoptosis is a crucial pathway in neuronal cell death in AD patients. 4-Hydroxynonenal (HNE), one of the aldehydic products of membrane lipid peroxidation, is reported to be elevated in the brains of AD patients and mediates the induction of neuronal apoptosis in the presence of oxidative stress. In this study, we investigated the HNE-induced apoptosis mechanism and the protective effects of the cocoa procyanidin fraction (CPF) and its major antioxidant procyanidin B2 against the apoptosis induced by HNE in rat pheochromocytoma (PC12) cells. HNE-induced nuclear condensation and increased sub-G1 fraction, both of which are markers of apoptotic cell death, were inhibited by CPF and procyanidin B2. Intracellular reactive oxygen species (ROS) accumulation was attenuated by pretreatment with CPF and procyanidin B2. CPF and procyanidin B2 also prevented HNE-induced poly(ADP-ribose) polymerase cleavage, antiapoptotic protein (Bcl-2 and Bcl-X(L)) down-regulation, and caspase-3 activation. Activation of c-Jun N-terminal protein kinase (JNK) and mitogen-activated protein kinase kinase 4 (MKK4) was attenuated by CPF and procyanidin B2. Moreover, CPF and procyanidin B2 bound directly to MKK4 and inhibited its activity. Data obtained with SP600125, a selective inhibitor of JNK, revealed that JNK is involved in HNE-induced apoptosis through the inhibition of PARP cleavage and caspase-3 activation in PC12 cells. Collectively, these results indicate that CPF and procyanidin B2 protect PC12 cells against HNE-induced apoptosis by blocking MKK4 activity as well as ROS accumulation.

S-allylcysteine scavenges singlet oxygen and hypochlorous acid and protects LLC-PK1 cells of potassium dichromate-induced toxicity

It has been found that S-allylcysteine (SAC), a garlic-derived compound, has in vivo and in vitro antioxidant properties. In addition, it is known that SAC is able to scavenge different reactive oxygen or nitrogen species including superoxide anion (O(2)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radical (OH()), and peroxynitrite anion (ONOO(-)) although the IC(5O) values for each reactive species has not been calculated and the potential ability of SAC to scavenge singlet oxygen ((1)O(2)) and hypochlorous acid (HOCl) has not been explored. The purposes of this work was (a) to explore the potential ability of SAC to scavenge (1)O(2) and HOCl, (b) to further characterize the O(2)(-), H(2)O(2), OH(), and ONOO(-) scavenging ability of SAC by measuring the IC(50) values using in vitro assays, and (c) to explore the potential ability of SAC to ameliorate the potassium dichromate (K(2)Cr(2)O(7))-induced cytotoxicity in LLC-PK1 cells in which oxidative stress is involved. The scavenging activity was compared against the following reference compounds: N-acetylcysteine for O(2)(-), sodium pyruvate for H(2)O(2), dimethylthiourea for OH(), lipoic acid and glutathione for (1)O(2), lipoic acid for HOCl, and penicillamine for ONOO(-). It was found that SAC was able to scavenge concentration-dependently all the species assayed with the following IC(5O) (mean+/-SEM, mM): O(2)(-) (14.49+/-1.67), H(2)O(2) (68+/-1.92), OH() (0.68+/-0.06), (1)O(2) (1.93+/-0.27), HOCl (2.86+/-0.15), and ONOO(-) (0.80+/-0.05). When the ability of SAC to scavenge these species was compared to those of the reference compounds it was found that the efficacy of SAC (a) to scavenge O(2)(-), H(2)O(2), OH(), and ONOO(-) was lower, (b) to scavenge HOCl was similar, and (c) to scavenge (1)O(2) was higher. In addition, it was found that SAC was able to prevent K(2)Cr(2)O(7)-induced toxicity in LLC-PK1 cells in culture. It was showed for the first time that SAC is able to scavenge (1)O(2) and HOCl and to ameliorate the K(2)Cr(2)O(7)-induced toxicity.

Anti-amyloidogenic activity of S-allyl-L-cysteine and its activity to destabilize Alzheimer's beta-amyloid fibrils in vitro

Alzheimer's disease involves Abeta accumulation, oxidative damage and inflammation and there is currently no clinically accepted treatment to stop its progression. Its risk is known to reduce with increased consumption of antioxidant and anti-inflammatory agents. Fibrillar aggregates of Abeta are major constituents of the senile plaques found in the brains of AD patients and have been related to AD neurotoxicity. It is reported that SAC (S-allyl-l-cysteine), a water-soluble organosulfur component present in garlic is known to prevent cognitive decline by protecting neurons from Abeta induced neuronal apoptosis. Hence, we investigated the effects of SAC on Abeta aggregation by employing Thioflavin-T, transmission electron microscopy, SDS-PAGE, size exclusion-HPLC. Under aggregating conditions in vitro, SAC dose-dependently inhibited Abeta fibrillation and also destabilized preformed Abeta fibrils. Further, Circular dichroism and fluorescence quenching studies supported the binding ability of SAC to Abeta and inducing a partially folded conformation in Abeta. The 3D structure of Abeta-SAC complex was also predicted employing automated docking studies.

Distinct mechanism of cell death is responsible for tunicamycin-induced ER stress in SK-N-SH and SH-SY5Y cells

In order to elucidate underlying mechanism of cell death pathways in neuronal cells in humans, we studied responsible pathways involved in the endoplasmic reticulum (ER) stress-induced cell death in neuroblastoma cells, SK-N-SH and its neuroblast-type subclone SH-SY5Y cells. A time-dependent induction of ER chaperons, glucose regulated protein (GRP)78 and GRP94, was observed after treatment with tunicamycin (TM), and cell death was also induced concomitantly in both cells. Although the pro-caspase-12-like protein was defined in both cells, a decrease in the protein was observed in only SH-SY5Y cells after exposure to TM. In contrast, pro-caspase-4 was detected in only SK-N-SH cells, and the cleaved-form was induced by the treatment with TM. A caspase-4 inhibitor, Z-LEVD-FMK attenuated TM-induced cell death in SK-N-SH cells. Calpain- and caspase-3-mediated proteolysis of alpha II-spectrin was also increased after the treatment with TM in both cells. A calpain inhibitor, calpeptin, repressed TM-induced cell death in only SK-N-SH cells. GADD153/C/EBP homologous protein (CHOP) was significantly induced after exposure to TM in only SH-SY5Y cells and RNA interference to GADD153/CHOP repressed TM-induced cell death. These results demonstrate that induction of GADD153/CHOP plays a pivotal role in mechanism of ER stress-induced cell death in SH-SY5Y cells, on the other hand, cleavage of pro-caspase-4 by activation of calpain play a crucial role in SK-N-SH cells. It is also suggested that the relevance of caspase-4 to ER stress is cell-specific even between human-origin cell lines.

Amyloid beta-protein potentiates tunicamycin-induced neuronal death in organotypic hippocampal slice cultures

We have assessed amyloid beta protein (Abeta)-induced neurotoxicity, with and without added tunicamycin (TM), an inhibitor of N-glycosylation in the endoplasmic reticulum (ER), in rat organotypic hippocampal slice cultures (OHCs). In the rat OHCs cultured for 3 weeks, there was little neurotoxicity after treatment with Abeta(25-35) (25 microM) alone for 48 h. However, with TM alone, concentration-dependent neuronal death was observed at concentrations between 20 and 80 microg/mL. When amyloid-beta protein was combined with tunicamycin (Abeta+TM), cell death was more acute than with TM alone. Western blot analysis revealed that calpain activity and the active forms of caspase-12 and caspase-3 was increased after exposure to Abeta+TM as compared with exposure to TM alone. In contrast, the levels of glucose regulated protein (GRP)94, GRP78 and C/EBP homologous protein (CHOP) were not changed in the presence of Abeta. Abeta potentiation of TM neurotoxicity was reversibly blocked by S-allyl-L-cysteine (SAC), an organosulfur compound purified from aged garlic extract, and the L-type calcium channel blocker, nifedipine, in a restricted neuronal area of the OHCs. Simultaneously applied SAC also reversed the increases in calpain activity and the active forms of caspase-12 and caspase-3 by Abeta+TM with no change in the increased levels of GRP94, GRP78 and CHOP. These data indicate that Abeta facilitates the calpain-caspase-12-caspase-3 pathway, thus potentiating TM-induced neuronal death in the hippocampus.

Role of caspase-12 in amyloid beta-peptide-induced toxicity in organotypic hippocampal slices cultured for long periods

Amyloid beta (Abeta) toxicity has been implicated in cell death in the hippocampus, but its specific mechanisms are poorly understood. In this study, Abeta-induced cell death was investigated in organotypic hippocampal slice cultures (OHCs) that were cultured for various periods in vitro. There were no obvious histological differences among slices cultured for 3 to 7 weeks in vitro. Although there was little neurotoxicity after treatment with Abeta25-35 in OHCs cultured for relatively shorter periods (3-5 weeks), age-dependent cell death was evident in OHCs cultured for relatively longer periods (6-7 weeks) after exposure to Abeta25-35. In OHCs cultured for 7 weeks, S-allyl-L-cysteine (SAC), a component of aged garlic extract, protected the cells in areas CA1 and CA3 and the dentate gyrus from Abeta25-35-induced toxicity. The immunoreactivity of cleaved caspase-12 was increased whereas that of glucose-regulated protein 78 was not altered after exposure to Abeta25-35. The increases in the cleaved caspase-12 were also reversed by simultaneously applied SAC. These results suggest that OHCs cultured for relatively longer periods are more susceptible to Abeta-induced toxicity and that the Abeta-induced cell death involves caspase-12-dependent pathways. It is also suggested that SAC is able to protect against the Abeta-induced neuronal cell death through the inhibition of the caspase-12-dependent pathway.

N-acetylcysteine selectively protects cerebellar granule cells from 4-hydroxynonenal-induced cell death

4-hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, has been shown to induce neurotoxicity accompanied by multiple events. To clarify mechanisms of neuroprotective compounds on HNE-induced toxicity, the protective effects of N-acetylcysteine (NAC), alpha-tocopherol (TOC), ebselen and S-allyl-L-cysteine (SAC) were compared in cerebellar granule neurons. The decrease in MTT reduction induced by HNE was significantly suppressed by pretreatment of the neurons with 1000 microM NAC or 10 and 100 microM TOC; however, lactate dehydrogenase (LDH) release and propidium iodide (PI) fluorescence studies revealed that neuronal death was suppressed by NAC but not by TOC. Treatment of these neurons with HNE resulted in a drastic reduction of mitochondrial membrane potential, and this reduction was also prevented by NAC but not by TOC. Ebselen and SAC, a garlic compound, were unable to protect these neurons against HNE-induced toxicity. Pretreatment with NAC also prevented HNE-induced depletion of intracellular glutathione (GSH) levels in these neurons. These results suggest that NAC, but not other antioxidants such as TOC, SAC and ebselen, exerts significant protective effects against HNE-induced neuronal death in cerebellar granule neurons, and that this neuroprotective effect is due, at least in part, to preservation of mitochondrial membrane potential and intracellular GSH levels.

Comparative study of endoplasmic reticulum stress-induced neuronal death in rat cultured hippocampal and cerebellar granule neurons

In this study, experiments were performed to characterize further the pathways responsible for neuronal death induced by endoplasmic reticulum (ER) stress in cultured hippocampal neurons (HPN) and cerebellar granule neurons (CGN) using tunicamycin (TM) and amyloid beta-peptide (Abeta). Exposure of HPN to Abeta or TM resulted in a time-dependent increase in the expression of 78-kDa glucose-regulated protein (GRP78) and caspase-12, an ER-resident caspase. In contrast, in CGN, although a drastic increase in the expression of GRP78 was found as was the case in HPN, no up-regulation of caspase-12 was detected. These results were consistent with immunohistochemical results that there were far lower number of caspase-12-positive cells in the cerebellum than in the cerebral cortex and hippocampus, and that caspase-12-positive cells were not identified in the external granule cell layer of the cerebellum of P7 rats. In CGN, a significant increase in the expression of C/EBP homologous protein (CHOP) protein was detected after exposure to Abeta or TM, whereas no such an increase in the protein expression was observed in HPN. In addition, S-allyl-L-cysteine (SAC), an organosulfur compound purified from aged garlic extract, protected neurons against TM-induced neurotoxicity in HPN but not in CGN, as in the case of Abeta-induced neurotoxicity. These results suggest that the pathway responsible for neuronal death induced by Abeta and TM in HPN differs from that in CGN, and that a caspase-12-dependent pathway is involved in HPN while a CHOP-dependent pathway is involved in CGN in ER stress-induced neuronal death.

4-Hydroxynonenal modulates the long-term potentiation induced by L-type Ca2+ channel activation in the rat dentate gyrus in vitro

Increased oxyradical production and membrane lipid peroxidation (MLP) occur under physiological and degenerative conditions in neurons. We investigated whether 4-hydroxynonenal (4HN), one of the membrane lipid peroxidation products, affects long-term potentiation (LTP) in the rat dentate gyrus in vitro. Treatment of hippocampal slices with 4HN (10 microM) enhanced LTP without affecting basal evoked potentials. The enhancement was completely inhibited by 2 microM nifedipine, a blocker of L-type Ca2+ channels. In cultured dentate gyrus neurons, treatment of the cells with 4HN for 24 h resulted in a significant amount of cell death that was detoxified by glutathione, whereas short-term treatment with 4HN (< or = 6 h) had no effect. Nifedipine partially but significantly suppressed the 4HN-induced cell death. These results suggest that 4HN modulates LTP and induces delayed cell death through L-type Ca2+ channel activation in the dentate gyrus. 4HN thereby plays an important role in both physiological and pathophysiological events in the hippocampus.

Modulation of voltage-gated Ca2+ current by 4-hydroxynonenal in dentate granule cells

Although recent studies have suggested that dentate granule cells play a key role in hippocampal functions, electrophysiological properties in these cells have not been sufficiently explored. In the present study, modification of voltage-gated Ca2+ channels by 4-hydroxynonenal (4HN), a major aldehydic product of membrane lipid peroxidation, in cultured dentate granule cells was examined using the whole-cell patch clamp technique. When whole-cell voltage clamp was applied, the cells exhibited a high-voltage-activated Ca2+ current, which was totally sensitive to 30 microM Cd2+ and partially sensitive to 2 microM nifedipine. 4HN enhanced the Ca2+ current in these cells. When L-type Ca2+ channels were blocked by application of nifedipine, the enhancement was completely canceled, whereas application of omega-conotoxin-GVIA or omega-agatoxin-IVA, blockers of N- and P/Q-type Ca2+ channels, respectively, had no effect. These results suggest that 4HN modulates L-type Ca2+ channels in the dentate granule cells, and thereby plays a role in the physiological and pathophysiological responses of these cells to oxidative stress.

Hydrogen peroxide modulates whole cell Ca2+ currents through L-type channels in cultured rat dentate granule cells

Modification of voltage-gated Ca(2+) channels by hydrogen peroxide, a membrane-permeable form of reactive oxygen species, in cultured dentate granule cells was examined using the whole cell patch clamp technique. Pretreatment with hydrogen peroxide (1 and 10 microM) for 2 h enhanced the Ca(2+) current without affecting its voltage dependence. The enhancement was completely cancelled by 1 mM glutathione, an antioxidant, and 2 microM nifedipine, an L-type Ca(2+) channel blocker. In contrast, the enhancement of the Ca(2+) current was not mimicked by pretreatment with 10 microg/ml tunicamycin, an endoplasmic reticulum stressor. These results suggest that oxidative stress induced by hydrogen peroxide selectively regulates the activity of L-type Ca(2+) channels.

S-allyl-L-cysteine selectively protects cultured rat hippocampal neurons from amyloid beta-protein- and tunicamycin-induced neuronal death

S-allyl-L-cysteine (SAC), one of the organosulfur compounds found in aged garlic extract, has been shown to possess various biological effects including neurotrophic activity. In our previous experiments, we found that SAC could protect against amyloid beta-protein (Abeta)- and tunicamycin-induced cell death in differentiated PC12 cells. In the study described here, we characterized the neuronal death induced by Abeta, 4-hydroxynonenal (HNE), tunicamycin, and trophic factor deprivation, and investigated whether and how SAC could prevent this in cultured rat hippocampal neurons. Treatment with SAC protected these cells against Abeta- and tunicamycin-induced neuronal death, which is mediated predominantly through caspase-12-dependent pathway in a concentration-dependent manner. In contrast, it afforded no protection against HNE- and trophic factor-deprivation-induced cell death, which has been shown to be mediated by caspase-3-dependent pathway. SAC also attenuated the Abeta-induced increase of intracellular reactive oxygen species in hippocampal neurons. SAC had no effect on Abeta-induced cell death in cultured cerebellar granule neurons, which was prevented by a caspase-3 inhibitor. These results suggest that SAC could protect against the neuronal cell death that is triggered by ER dysfunction in the hippocampus, and that it has no effect on neuronal cell death that is dependent upon the caspase-3 mediated pathway.

The Peptide KLVFF-K6Promotes β-Amyloid(1–40) Protofibril Growth by Association but Does Not Alter Protofibril Effects on Cellular Reduction of 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide (MTT)

The peptide KLVFF-K6 was observed by Lowe et al. to simultaneously enhance amyloid beta-protein (Abeta) fibrillogenesis and decrease cellular toxicity, as measured in a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. It was postulated that accelerated Abeta aggregation and precipitation induced by KLVFF-K6 may lead to an increase in less toxic insoluble fibrils at the expense of more toxic soluble protofibrils. In a previous study, we distinguished between two modes of protofibril growth: elongation by monomer deposition and direct protofibril-protofibril association. These growth mechanisms could be resolved by varying Abeta monomer and NaCl concentrations. Using assays designed to isolate these distinct modes of protofibril growth, we report here that larger Abeta aggregates formed in the presence of KLVFF-K6 resulted from enhanced protofibril association. 3H-Radiomethylated KLVFF-K6 bound to associated protofibrils with an apparent Kd of 180 nM, and concentrations of free [3H]KLVFF-K6 in this range were sufficient to convert soluble protofibrils to sedimentable fibrils. However, promotion of Abeta protofibril association by KLVFF-K6 had no effect on Abeta-induced decreases in cellular MTT reduction. Therefore, our data do not support the proposal that insoluble fibrils formed with KLVFF-K6 are less toxic than soluble protofibrils. KLVFF-K6 did not alter rates of protofibril elongation by monomer deposition. In contrast, when added to Abeta monomers isolated with the use of size-exclusion chromatography, KLVFF-K6 inhibited fibrillogenesis, as measured by thioflavin T fluorescence, and this inhibition was paralleled by a failure to alter cellular MTT reduction.

Neurotoxicity induced by amyloid beta-peptide and ibotenic acid in organotypic hippocampal cultures: protection by S-allyl-L-cysteine, a garlic compound

We have assessed amyloid-beta (Abeta)-induced neurotoxicity, with and without added ibotenic acid (IBO), a potent N-methyl-D-aspartate (NMDA) agonist, in an organotypic hippocampal slice culture (OHC). In the OHC, there was little neurotoxicity after treatment with Abeta(25-35) (25 or 50 microM) alone for 48 h. However, with IBO alone neuronal death was observed in the pyramidal cell layer at low concentrations, and there was dramatic neuronal death at concentrations of 65 microM or more. When Abeta was combined with IBO (Abeta+IBO) there was more intense cell death than with IBO alone. S-Allyl-L-cysteine (SAC), one of the organosulfur compounds having a thioallyl group in aged garlic extract, was shown to protect the hippocampal neurons in the CA3 area and the dentate gyrus (DG) from the cell death induced by Abeta+IBO with no change in the CA1 area. Although L-glutamate (500 microM) potentiated the degree of IBO-induced neuronal death, it attenuated the Abeta+IBO-induced neuronal death in both the CA3 area and the DG with no obvious effect on the CA1 area. These results suggest that Abeta+IBO induces extensive neuronal death, and that SAC and L-glutamate protect cells from death in specific areas of the hippocampus. In addition, inhibition using a pan-caspase inhibitor, z-VAD-fmk, only provided partial protection from Abeta+IBO-induced toxicity for the neurons in the CA3 area. These results suggest that multiple mechanisms may be involved in Abeta+IBO-induced neuronal death in the OHC.