Tea catechins protect against lead-induced ROS formation, mitochondrial dysfunction, and calcium dysregulation in PC12 cells

Studying the effects of lead on DNA fragmentation and proapoptotic bax and antiapoptotic bcl-2 protein expression in PC12 cells

ABSTRACT The nervous system is one of the most important targets of lead poisoning. Despite decades of study, the exact mechanism of lead toxicity has not been fully elucidated. One of the suggested mechanisms of lead toxicity is induction of apoptosis, which has not been shown yet in some neuronal cells such as pheochromocytoma cells (PC12). Therefore, the present study sought to examine the effect of lead poisoning on apoptosis in PC12 cells as a suitable model of neuronal cell study. The present results showed that lead could induce toxicity in PC12 cells after 24 hours with as little as 1 muM in a concentration-dependent manner. In Western blot analysis, the ratio of Bax/Bcl-2 protein expression in cells incubated with 3, 30, and 90 muM lead acetate significantly increased compared to controls. Additionally, a DNA laddering pattern in lead-treated cells was shown, which could indicate nuclear fragmentation. It might be concluded that lead could cause PC12 cell death, in which apoptosis or programmed cell death plays an important role.

Phytochemical profile and nutraceutical value of old and modern common wheat cultivars

Among health-promoting phytochemicals in whole grains, phenolic compounds have gained attention as they have strong antioxidant properties and can protect against many degenerative diseases. Aim of this study was to profile grain phenolic extracts of one modern and five old common wheat (Triticum aestivum L.) varieties and to evaluate their potential antiproliferative or cytoprotective effect in different cell culture systems.Wheat extracts were characterized in terms of antioxidant activity and phenolic composition (HPLC/ESI-TOF-MS profile, polyphenol and flavonoid contents). Results showed that antioxidant activity (FRAP and DPPH) is mostly influenced by flavonoid (both bound and free) content and by the ratio flavonoids/polyphenols. Using a leukemic cell line, HL60, and primary cultures of neonatal rat cardiomyocytes, the potential antiproliferative or cytoprotective effects of different wheat genotypes were evaluated in terms of intracellular reactive oxygen species levels and cell viability. All tested wheat phenolic extracts exerted dose-dependent cytoprotective and antiproliferative effects on cardiomyocytes and HL60 cells, respectively. Due to the peculiar phenolic pattern of each wheat variety, a significant genotype effect was highlighted. On the whole, the most relevant scavenging effect was found for the old variety Verna. No significant differences in terms of anti-proliferative activities among wheat genotypes was observed.Results reported in this study evidenced a correspondence between the in vitro antioxidant activity and potential healthy properties of different extracts. This suggests that an increased intake of wheat grain derived products could represent an effective strategy to achieve both chemoprevention and protection against oxidative stress related diseases.

Oxidative stress: a possible mechanism for lead-induced apoptosis and nephrotoxicity

Lead-induced nephrotoxicity is a human health hazard problem. In this study, Human mesangial cells (HMCs) were treated with different concentration of lead acetate (5, 10, 20 μmol/l) in order to investigate the oxidative stress and apoptotic changes. It was revealed that lead acetate could induce a progressive loss in HMCs viability together with a significant increase in the number of apoptotic cells using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium (MTT) assay and flow cytometry, respectively. The apoptotic morphological changes induced by lead exposure in HMCs were demonstrated by PI-Hochest33342 staining. A DNA laddering pattern in lead-treated cells was shown, which could indicate nuclear fragmentation. In addition, lead acetate significantly increased the levels of malondialehyde (MDA) content and lactate dehydrogenase (LDH) activity. Therefore, it might be concluded that lead could promote HMCs' oxidative stress and apoptosis, which may be the chief mechanisms of lead-induced nephrotoxicity.

Proliferation potential of human amniotic fluid stem cells differently responds to mercury and lead exposure

There are considerable gaps in our knowledge on cell biological effects induced by the heavy metals mercury (Hg) and lead (Pb). In the present study we aimed to explore the effects of these toxicants on proliferation and cell size of primary human amniotic fluid stem (AFS) cells. Monoclonal human AFS cells were incubated with three dosages of Hg and Pb (single and combined treatment; ranging from physiological to cytotoxic concentrations) and the intracellular Hg and Pb concentrations were analyzed, respectively. At different days of incubation the effects of Hg and Pb on proliferation, cell size, apoptosis, and expression of cyclins and the cyclin-dependent kinase inhibitor p27 were investigated. Whereas we found Hg to trigger pronounced effects on proliferation of human AFS cells already at low concentrations, anti-proliferative effects of Pb could only be detected at high concentrations. Exposure to high dose of Hg induced pronounced downregulation of cyclin A confirming the anti-proliferative effects observed for Hg. Co-exposure to Hg and Pb did not cause additive effects on proliferation and size of AFS cells, and on cyclin A expression. Our here presented data provide evidence that the different toxicological effects of Pb and Hg on primary human stem cells are due to different intracellular accumulation levels of these two toxicants. These findings allow new insights into the functional consequences of Pb and Hg for mammalian stem cells and into the cell biological behavior of AFS cells in response to toxicants.

Protective effect of catechin in type I Gaucher disease cells by reducing endoplasmic reticulum stress

Gaucher disease (GD) is the most common lysosomal storage disorder (LSD) and is divided into three phenotypes, I, II, and III. Type I is the most prevalent form and has its onset in adulthood. The degree of endoplasmic reticulum (ER) stress is one of the factors that determine GD severity. It has recently been reported that antioxidants reduce ER stress and apoptosis by scavenging the oxidants that cause oxidative stress. For this report, we investigated the possibility that catechin can act on type I GD patient cells to alleviate the pathogenic conditions of GD. We treated GD cells with catechin and examined the expression level of GRP78/BiP (an ER stress marker) by western blots and fluorescence microscopy, the proliferation rate of GD cells, and scratch-induced wound healing activity. Our results show that catechin reduces the expression level of GRP78/BiP, leads to cell proliferation rates of GD cells similar levels to normal cells, and improves wound healing activity. We conclude that catechin protects against ER stress in GD cells and catechin-mediated reductions in ER stress may be associated with enhanced cell survival.

Comparative evaluation of N-acetylcysteine (NAC) and N-acetylcysteine amide (NACA) on glutamate and lead-induced toxicity in CD-1 mice

Recent studies indicate that there is interaction between the glutamatergic neurotransmitters system and lead neurotoxicity. Previously, we have demonstrated the potential effects of glutamate in lead-induced cell death in PC12 cells and the protective role of the novel thiol antioxidant, N-acetylcysteine amide (NACA). The current study (1) investigated the potential effects of glutamate on lead exposed CD-1 mice, (2) evaluated the protective effects of NACA against glutamate and lead toxicity in CD-1 mice, and (3) compared the results with N-aceytylcysteine (a well-known thiol antioxidant). Oxidative stress parameters, including glutathione (GSH), oxidized glutathione (GSSG), GSH/GSSG, and malondialdehyde (MDA) levels, were evaluated. Blood and tissue lead levels, glutamate/glutamine (Glu/Gln) ratios, GS activity, and phospholipase-A(2) (PLA(2)) were also analyzed. Results indicated that lead and glutamate decreased GSH levels in the red blood cells, brains, livers, and kidneys. Exposure to glutamate and lead elevated the MDA levels and PLA(2) activity. NACA and N-acetylcysteine (NAC) provided protection against the detrimental effects of lead by decreasing the blood and tissue lead levels, restoring intracellular GSH levels, and decreasing the MDA levels. NACA and NAC also increased the GS activity thereby decreasing Glu/Gln levels. However, NACA appeared to have better chelating and antioxidant properties than NAC, due to its higher liphophilicity and its ability to cross the blood-brain barrier.

Protective effect of C(60) -methionine derivate on lead-exposed human SH-SY5Y neuroblastoma cells

Oxidative stress has been considered as one of the possible mechanisms leading to the neurotoxicity of lead. One of the effective ways to prevent cellular damage after lead exposure is using antioxidants. In this paper, a novel C(60) -methionine derivate (FMD), a fullerene molecule modified with methionine, was synthesized. The protective effect of FMD on lead-exposed human SH-SY5Y neuroblastoma cells was investigated. In this research, after incubating with 500 µm Pb acetate alone for 72 h, the cells had undergone a series of biological changes including viability loss, apoptotic death, the depletion of glutathione (GSH), the peroxidation of membrane lipid and DNA damage. Pretreatment with FMD before lead exposure could improve cell survival, increase the GSH level, reduce malondialdehyde content and attenuate DNA damage without obvious toxicity. In addition, the protective effects of FMD were proven to be greater than those of other two C(60) -amino acid derivates, β-alanine C(60) derivate and cystine C(60) derivate, which have been confirmed in our previous work to be able to protect rat pheochromocytoma PC12 cells from hydrogen dioxide-induced oxidative injuries. These observations suggest that FMD may serve as a potential antioxidative and neuroprotective agent in the prevention of lead intoxication.

Effect of lead on oxidative stress, Na+K+ATPase activity and mitochondrial electron transport chain activity of the brain of Clarias batrachus L

The present invivo study was designed to elucidate the toxic effect of lead on oxidative stress, Na(+)K(+)ATPase and mitochondrial electron transport chain activity of the brain of Clarias batrachus. The fish were exposed to 10 and 20% of the derived 96 h LC(50) value, 37.8 and 75.6 mg L(-1), respectively, and sampled on 20, 40 and 60 days. Exposure of fish brain to lead demonstrated an increased production of reactive oxygen species, increased lipid peroxidation, loss of protein thiol groups in synaptosomal fraction with the decreased activity of Na(+)K(+)ATPase, partial inactivation of mitochondrial electron transport chain activity and energy depletion. However, no change in protein carbonyl content in synaptosomal fraction was observed due to lead exposure. Concluding the results of our investigation we suggest that lead exposure induces oxidative stress in the brain of Clarias batrachus and the decline in Na(+)K(+)ATPase activity was presumeably mediated by the combined action of lipid peroxidation and deficient mitochondrial electron transport chain activity.

Green tea epigallocatechin 3-gallate accumulates in mitochondria and displays a selective antiapoptotic effect against inducers of mitochondrial oxidative stress in neurons

Epigallocatechin-3-gallate (EGCG) is a major flavonoid component of green tea that displays antiapoptotic effects in numerous models of neurotoxicity. Although the intrinsic free radical scavenging activity of EGCG likely contributes to its antiapoptotic effect, other modes of action have also been suggested. We systematically analyzed the antiapoptotic action of EGCG in primary cultures of rat cerebellar granule neurons (CGNs). The dose-dependent protective effects of EGCG were determined after coincubation with eight different stimuli that each induced neuronal apoptosis by distinct mechanisms. Under these conditions, EGCG provided significant neuroprotection only from insults that induce apoptosis by causing mitochondrial oxidative stress. Despite this selective antiapoptotic effect, EGCG did not significantly alter the endogenous activities or expression of Mn(2+)- superoxide dismutase, glutathione peroxidase, Nrf2, or Bcl-2. Subfractionation of CGNs after incubation with (3)H-EGCG revealed that a striking 90-95% of the polyphenol accumulated in the mitochondrial fraction. These data demonstrate that EGCG selectively protects neurons from apoptosis induced by mitochondrial oxidative stress. This effect is likely due to accumulation of EGCG in the mitochondria, where it acts locally as a free radical scavenger. These properties of EGCG make it an interesting therapeutic candidate for neurodegenerative diseases involving neuronal apoptosis triggered by mitochondrial oxidative stress.

Mechanism of teratogenesis: Electron transfer, reactive oxygen species, and antioxidants

Teratogenesis has been a topic of increasing interest and concern in recent years, generating controversy in association with danger to humans and other living things. A veritable host of chemicals is known to be involved, encompassing a wide variety of classes, both organic and inorganic. Contact with these chemicals is virtually unavoidable due to contamination of air, water, ground, food, beverages, and household items, as well as exposure to medicinals. The resulting adverse effects on reproduction are numerous. There is uncertainty regarding the mode of action of these chemicals, although various theories have been advanced, e.g., disruption of the central nervous system (CNS), DNA attack, enzyme inhibition, interference with hormonal action, and insult to membranes, proteins, and mitochondria. This review provides extensive evidence for involvement of oxidative stress (OS) and electron transfer (ET) as a unifying theme. Successful application of the mechanistic approach is made to all of the main classes of toxins, in addition to large numbers of miscellaneous types. We believe it is not coincidental that the vast majority of these substances incorporate ET functionalities (quinone, metal complex, ArNO2, or conjugated iminium) either per se or in metabolites, potentially giving rise to reactive oxygen species (ROS) by redox cycling. Some categories, e.g., peroxides and radiation, appear to generate ROS by non-ET routes. Other mechanisms are briefly addressed; a multifaceted approach to mode of action appears to be the most logical. Our framework should increase understanding and contribute to preventative measures, such as use of antioxidants.

Lead-induced apoptosis in PC 12 cells: involvement of p53, Bcl-2 family and caspase-3

It has been reported that lead could induce apoptosis in a variety of cell types. Although mitochondrion is regarded as the most pertinent pathway in mediating apoptosis, the exact mechanisms of lead-induced apoptosis are still largely unknown. Furthermore, there is little information about expressions and regulations of Bax, Bcl-2, and p53 in lead-induced apoptosis, which are critical regulators of mitochondrial stability. The present study was undertaken to determine whether lead could induce DNA damage and apoptosis in PC 12 cells, and the involvement of Bax, Bcl-2, p53, and caspase-3 in this process. The results showed that lead could induce DNA damage and apoptosis in PC 12 cells, accompanying with upregulation of Bax and downregulation of Bcl-2. Additionally, the expression of p53 increased, and caspase-3 was activated. Therefore, it suggests that lead can induce activation of p53 by DNA damage, which may lead to imbalance of Bax/Bcl-2 and mitochondrial dysfunction. Subsequently, after activation of caspase-3, lead-induced apoptosis occurres.

Glutamate-induced oxidative stress, but not cell death, is largely dependent upon extracellular calcium in mouse neuronal HT22 cells

Elucidating the relationship of glutamate-induced Ca2+ flux and oxidative death of neuronal cells may be of great relevance for neurodegenerative diseases in human beings. Mouse hippocampal HT22 cells provide a model system to study this relationship at the molecular level. Here we show that stimulation of HT22 cells with 5 mM glutamate is cytotoxic. Glutamate-induced cytotoxicity was associated with the generation of reactive oxygen species (ROS) and activation of the death executioner caspases 1 and 3. Treatment of HT22 cells with the calcium chelator, EGTA, and the calcium channel blocker, CoCl2, revealed that glutamate-induced cell death was dependent, in part, on glutamate-induced Ca2+ influx from extracellular stores. However, activation of caspases 1 and 3 and death of HT22 cells were also observed when Ca2+ was lacking in the extracellular milieu and ROS production abrogated. These findings led us to conclude that glutamate-induced death of mouse HT22 cells utilizes a complex mechanism that relies only in part on Ca2+ influx and ROS production. Additional studies are warranted to evaluate glutamate-induced death mechanisms that operate independently of Ca2+ influx and generation of ROS.

Calcium and Reactive Oxygen Species Mediated Zn2+-Induced Apoptosis in PC12 Cells

The release of excessive Zn(2+) from presynaptic boutons into extracellular regions contributes to neuronal apoptotic events, which result in neuronal cell death. However, the mechanisms of Zn(2+)-induced neuronal cell death are still unclear. Therefore, we investigated the dynamics of intracellular Zn(2+), calcium, and reactive oxygen species in PC12 cells. The addition of Zn(2+) produced cell death in a concentration- and time-dependent manner. (45)Ca(2+) influx occurred just after the treatment with Zn(2+), although subsequent hydroxyl radical ((*)OH) production did not begin until 3 h after Zn(2+) exposure. (*)OH production was significantly attenuated in Ca(2+)-free medium or by L-type Ca(2+) channel antagonist treatment, but it was independent of the intracellular Zn(2+) content. Dantrolene treatment had no protective effects against Zn(2+)-induced cell death. Treatment with N-acetyl-L-cysteine blocked (*)OH generation and subsequent cell death. These data indicate that Ca(2+) influx and subsequent (*)OH production are critical events in Zn(2+)-induced toxicity in PC12 cells.

Study of correlation between lead-induced cytotoxicity and nitric oxide production in PC12 cells

Despite reduction in its exposure, lead remains a major health problem. The primary target of lead toxicity is the central nervous system. The cellular, intracellular and molecular mechanisms of lead neurotoxicity are numerous, such as induction of apoptosis and interfering with Ca2+ dependent enzyme like nitric oxide synthase (NOS). To investigate the cytotoxic effect of lead on rat pheochromocytoma (PC12) cells, as a suitable model for neuroscience study, and possible correlation between lead toxicity and nitric oxide (NO) production, this study was performed. The current results showed that lead could induce cytotoxicity as well as NO production in a dose dependent manner in PC12 cells after 24h. The cytotoxicity was positively correlated with increased NOx (nitrite and nitrate) production in these cells. L-NAME, a NOS inhibitor, treatment (2.5 mM) could reverse this cytotoxicity. It can be concluded that lead-induced cytotoxicity in PC12 cells could partly be mediated by higher NO production.

Mechanisms of action of green tea catechins, with a focus on ischemia-induced neurodegeneration

Catechins are dietary polyphenolic compounds associated with a wide variety of beneficial health effects in vitro, in vivo and clinically. These therapeutic properties have long been attributed to the catechins' antioxidant and free radical scavenging effects. Emerging evidence has shown that catechins and their metabolites have many additional mechanisms of action by affecting numerous sites, potentiating endogenous antioxidants and eliciting dual actions during oxidative stress, ischemia and inflammation. Catechins have proven to modulate apoptosis at various points in the sequence, including altering expression of anti- and proapoptotic genes. Their anti-inflammatory effects are activated through a variety of different mechanisms, including modulation of nitric oxide synthase isoforms. Catechins' actions of attenuating oxidative stress and the inflammatory response may, in part, account for their confirmed neuroprotective capabilities following cerebral ischemia. The versatility of the mechanisms of action of catechins increases their therapeutic potential as interventions for numerous clinical disorders. However, more epidemiological and clinical studies need to be undertaken for their efficacy to be fully elucidated.