Lipid peroxidation-mediated cytotoxicity and DNA damage in U937 cells

Membrane lipid peroxidation processes yield products that may react with DNA and proteins to cause oxidative modifications. In the present study, we evaluated lipid peroxidation-mediated cytotoxicity and oxidative DNA damage in U937 cells. Upon exposure of U937 cells to tert-butylhydroperoxide (t-BOOH) and 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH), which induce lipid peroxidation in membranes, the cells exhibited a reduction in viability and an increase in the endogenous production of reactive oxygen species (ROS), as measured by the oxidation of 2',7'-dichlorodihydrofluorescein. In addition, a significant decrease in the intracellular GSH level and the activities of major antioxidant enzymes were observed. We also observed lipid peroxidation-mediated oxidative DNA damage, reflected by an increase in 8-OH-dG level and loss of the ability of DNA to renature. When the cells were pretreated with the antioxidant N-acetylcysteine (NAC) or the spin trap alpha-phenyl-N-t-butylnitrone (PBN), lipid peroxidation-mediated cytotoxicity in U937 cells was protected. This effect seems to be due to the ability of NAC and PBN to reduce ROS generation induced by lipid peroxidation. These results suggest that lipid peroxidation resulted in a pro-oxidant condition of U937 cells by the depletion of GSH and inactivation of antioxidant enzymes, which consequently leads to a decrease in survival and oxidative damage to DNA. The results indicate that the peroxidation of lipid is probably one of the important intermediary events in oxidative stress-induced cellular damage.     

The mode of cisplatin-induced cell death in CYP2E1-overexpressing HepG2 cells: modulation by ERK, ROS, glutathione, and thioredoxin

In a previous study, E47 HepG2 cells that overexpress human CYP2E1 were shown to be more sensitive to cisplatin than C34 cells that do not express CYP2E1. In this study, we found that this sensitivity was due to an earlier activation of ERK in the E47 cells compared to the C34 cells. Glutathione depletion by L-buthionine sulfoximine (BSO) enhanced cisplatin cytotoxicity via increasing production of reactive oxygen species (ROS) and activation of ERK. In contrast, elevation of glutathione by glutathione ethyl ester (GSHE) decreased cisplatin/BSO cytotoxicity by decreasing ROS production and ERK activation. Inhibition of ERK activation by U0126 protected against cisplatin/BSO cytotoxicity via inhibiting ROS production but not restoring intracellular glutathione content. Examination of the mode of cell death showed that U0126 inhibited cisplatin-induced necrosis but not apoptosis. Cisplatin-induced apoptosis was caspases-dependent; BSO switched cisplatin-induced apoptosis to necrosis via decreasing activity of caspases, and GSHE switched cisplatin/BSO-induced necrosis back to apoptosis through maintaining activity of caspases. Similar to GSHE, U0126 partially switched cisplatin/BSO induced necrosis to apoptosis via restoring activity of caspases. Cisplatin lowered levels of thioredoxin, especially in the presence of BSO. Although U0126 failed in restoring intracellular glutathione levels, it restored thioredoxin levels, which maintain the activity of the caspases. These results suggest that thioredoxin can replace glutathione to promote the active thiol redox state necessary for caspase activity, and thus glutathione and thioredoxin regulate the mode of cisplatin toxicity in E47 cells via redox regulation of caspase activity.     

Involvement of N-acetylcysteine-sensitive pathways in ricin-induced apoptotic cell death in U937 cells

We have found that the antioxidant N-acetylcysteine (NAC) strongly inhibited ricin-induced apoptotic cell death in U937 cells (human myeloid leukemia), as judged by cytotoxicity, nuclear morphological change, and DNA fragmentation. Consistent with these observations, a significant depletion of cellular glutathione was observed in ricin-treated cells, and NAC prevented the decrease in cellular glutathione. On the other hand, among the caspase inhibitors tested, Z-Asp-CH2-DCB, which inhibited ricin cytotoxicity, also suppressed ricin-mediated glutathione depletion, while NAC did not affect the generation of caspase-3 like activity in ricin-treated cells. These results suggest that glutathione loss takes place downstream from caspase activation during the ricin-induced apoptotic process. Treatment with a specific inhibitor of glutathione biosynthesis, buthionine sulfoximine (BSO) failed to induce apoptosis, and had no effect on the overall extent of ricin-induced apoptosis, even though the glutathione level was decreased to less than 5% of the control level. However, NAC still protected against ricin-induced apoptosis in the BSO-treated cells. We conclude that glutathione loss is one of several apoptotic changes caused by ricin, but is not a sufficient factor for the progress of apoptosis. NAC may prevent ricin-induced apoptosis through maintaining an intracellular reducing condition by acting as a thiol supplier.     

Protective mechanisms of N‐acetyl‐cysteine against pyrrolizidine alkaloid clivorine‐induced hepatotoxicity

Pyrrolizidine alkaloid (PA) clivorine, isolated from traditional Chinese medicinal plant Ligularia hodgsonii Hook, has been shown to induce apoptosis in hepatocytes via mitochondrial‐mediated apoptotic pathway in our previous research. The present study was designed to observe the protection of N‐acetyl‐cysteine (NAC) on clivorine‐induced hepatocytes apoptosis. Our results showed that 5 mM NAC significantly reversed clivorine‐induced cytotoxicity via MTT and Trypan Blue staining assay. DNA apoptotic fragmentation analysis and Western‐blot results showed that NAC decreased clivorine‐induced apoptotic DNA ladder and caspase‐3 activation. Further results showed that NAC inhibited clivorine‐induced Bcl‐xL decrease, mitochondrial cytochrome c release and caspase‐9 activation. Intracellular glutathione (GSH) is an important ubiquitous redox‐active reducing sulfhydryl (? SH) tripeptide, and our results showed that clivorine (50 µM) decreased cellular GSH amounts and the ratio of GSH/GSSG in the time‐dependent manner, while 5 mM NAC obviously reversed this depletion. Further results showed that GSH synthesis inhibitor BSO augmented clivorine‐induced cytotoxicity, while exogenous GSH reversed its cytotoxicity on hepatocytes. Clivorine (50 µM) significantly induced cellular reactive oxygen species (ROS) generation. Further results showed that 50 µM Clivorine decreased glutathione peroxidase (GPx) activity and increased glutathione S transferase (GST) activity, which are both GSH‐related antioxidant enzymes. Thioredoxin‐1 (Trx) is also a ubiquitous redox‐active reducing (? SH) protein, and clivorine (50 µM) decreased cellular expression of Trx in a time‐dependent manner, while 5 mM NAC reversed this decrease. Taken together, our results demonstrate that the protection of NAC is major via maintaining cellular reduced environment and thus prevents clivorine‐induced mitochondrial‐mediated hepatocytes apoptosis. J. Cell. Biochem. 108: 424–432, 2009. © 2009 Wiley‐Liss, Inc.     

Intracellular glutathione regulates Andrographolide-induced cytotoxicity on hepatoma Hep3B cells

Abstract

Andrographolide (ANDRO), a diterpenoid lactone isolated from the traditional herbal plant Andrographis paniculata, was reported to induce apoptosis in hepatoma Hep3B cells in our previous study (Ji LL, Liu TY, Liu J, Chen Y, Wang ZT. Andrographolide inhibits human hepatoma-derived Hep3B cells growth through the activation of c-Jun N-terminal kinase. Planta Med 2007; 73: 1397–1401). The present investigation was carried out to observe whether cellular reduced glutathione (GSH) plays important roles in ANDRO-induced apoptosis. ANDRO initially increased intracellular GSH levels which then decreased later, while inhibition of cellular GSH synthesis by L-Buthionine-(S,R)-sulfoximine (BSO) augmented ANDRO-induced cytotoxicity and apoptosis in Hep3B cells. On the other hand, the thiol antioxidant dithiothreitol (DTT) rescued ANDRO-depleted cellular GSH, and abrogated ANDRO-induced cytotoxicity and apoptosis. Furthermore, BSO pretreatment augmented ANDRO-decreased expression of antioxidant protein thioredoxin 1 (Trx1), while DTT reversed this decrease. Further results showed that ANDRO increased the activity of the GSH-related antioxidant enzyme glutathione peroxidase (GPx) and the production of intracellular reactive oxygen species (ROS). Taken together, this study demonstrates that the intracellular redox system plays important roles in regulating the cytotoxicity of ANDRO on hepatoma Hep3B cells.     

Rapid and transient intracellular oxidative stress due to novel macrosphelides trigger apoptosis via Fas/caspase-8-dependent pathway in human lymphoma U937 cells

The ability of the derivatives of macrosphelides (MS) core (simplified 16-membered core structure of natural MS) to induce apoptosis in human lymphoma U937 cells was investigated. Of the five compounds examined, MS core with ketones at 8 and 14 positions (MS5) showed the highest potency to induce apoptosis, while another, MS3 with one ketone, was minimal potent. MS5 was found to induce apoptosis in the U937 cells in a time- and dose-dependent fashion, as confirmed by DNA fragmentation analysis. MS5 treated cells showed increase in intracellular reactive oxygen species (ROS), glutathione depletion, Bid activation and lipid peroxidation. Pretreatment of cells with pancaspase inhibitor resulted in the complete inhibition of MS5-induced apoptosis. N-Acetyl-l-cysteine (NAC) pretreatment resulted in the increase in glutathione concentration, reduction of intracellular ROS, complete inhibition of DNA fragmentation, mitochondrial membrane potential (MMP) collapse, Fas externalization and caspase-8 activation. Furthermore, MS5-induced oxidative stress also triggered transient increase in intracellular calcium ion ([Ca2+]i) concentration which was completely inhibited by NAC. Pretreatment with an intracellular Ca2+ chelator, BAPTA-AM reduced MS5-induced DNA fragmentation and caspase-8 activation while it has marginal effects on MMP collapse. Taken together our present data showed that a rapid increase in intracellular ROS by MS5 triggers apoptosis via the Fas/caspase-8-mediated mitochondrial pathway suggesting that the presence of diketone makes the compound more potent to induce apoptosis. These characteristics of MS5 will make it useful for therapeutic applications of targeted apoptosis.     

N-acetylcysteine increases apoptosis induced by H(2)O(2) and mo-antiFas triggering in a 3DO hybridoma cell line

N-Acetylcysteine (NAC) has been used as an antioxidant to prevent apoptosis triggered by different stimuli in different cell types. It is common opinion that cellular redox, which is largely determined by the ratio of oxidized and reduced glutathione (GSH), plays a significant role in the propensity of cells to undergo apoptosis. However, there are also contrasting opinions stating that intracellular GSH depletion or supplemented GSH alone are not sufficient to lead cells to apoptosis or conversely protect them. Unexpectedly, this study shows that NAC, even if it maintains the peculiar characteristics of an agent capable of reducing cell proliferation and increasing intracellular GSH content, increases apoptosis induced by H(2)O(2) treatment and mo-antiFas triggering in a 3DO cell line. We found that 24 h of NAC pre-treatment can shift cellular death from necrotic to apoptotic and determine an early expression of FasL in a 3DO cell line treated with H(2)O(2).     

Knockdown of Glutamate Cysteine Ligase Catalytic Subunit by siRNA Causes the Gold Nanoparticles-Induced Cytotoxicity in Lung Cancer Cells

Gold nanoparticles (GNPs) have shown promising medical applications in cancer treatment involved in the regulation of intracellular redox balance. Previously, we have reported that GNPs can trigger apoptosis and necrosis in human lung cancer cells (A549) when L-buthionine-sulfoximine (BSO) was used to decrease the expression of intracellular glutathione (GSH). Herein, we investigated the cytotoxicity of GNPs toward lung cancer cells under the glutamate cysteine ligase catalytic subunit (GCLC) was silenced by siRNA. Our results showed that GNPs cause apoptosis and necrosis in cells transfected with GCLC siRNA by elevating intracellular reactive oxygen species (ROS). These findings demonstrated that the regulation of glutathione synthesis by GCLC siRNA in A549 cells can initiate the gold nanoparticles-induced cytotoxicity.     

Induction of CD95 ligand and apoptosis by doxorubicin is modulated by the redox state in chemosensitive- and drug-resistant tumor cells.

Induction of CD95 ligand (CD95-L) may contribute to drug-induced apoptosis in chemosensitive leukemias and solid tumors. Here we report that induction of CD95-L and apoptosis by doxorubicin in leukemic and neuroblastoma cells is regulated by the redox state and reactive oxygen species (ROS). Preincubation of chemosensitive cells with antioxidants such as N-acetyl-cysteine (NAC) or glutathione (GSH), significantly reduced doxorubicin-induced apoptosis, hyperexpression of ROS, loss of mitochondrial membrane potential (DeltaPsim) and upregulation of CD95-L expression. Doxorubicin-resistant cells exhibited higher levels of GSH in comparison to chemosensitive cells and were deficient in hyperproduction of ROS, loss of DeltaPsim and upregulation of CD95-L in response to cytotoxic drugs. Downregulation of intracellular GSH concentrations reversed deficient drug-induced hyperproduction of ROS and CD95-L upregulation. In addition, overexpression of Bcl-XL in CEM cells blocked doxorubicin-triggered ROS and CD95-L expression. These findings suggest that induction of CD95-L by cytotoxic drugs is modulated by the cellular redox state and mitochondria derived ROS.     

Nanoceria protects from alterations in oxidative metabolism and calcium overloads induced by TNFα and cycloheximide in U937 cells: pharmacological potential of nanoparticles

The present study is aimed to determine the protective effect of a novel nanoparticle with antioxidant properties, nanoceria, on reactive oxygen species (ROS) production, and calcium signaling evoked by the tumor necrosis factor-alpha (TNFα) in combination with cycloheximide (CHX) on apoptosis in the human histiocytic lymphoma cell line U937. Our results show that treatment of U937 cells with 10 ng/mL TNFα in combination with 1 μg/mL CHX led to several Ca²⁺ alterations. These stimulatory effects on calcium signals were followed by intracellular ROS production and mitochondria membrane depolarization, as well as a time-dependent increase in caspase-8 and -9 activities. Our results show that the pretreatment with well known antioxidants such as trolox and N-acetyl cysteine (NAC) partially reduced the apoptotic effects due to the administration of TNFα plus cycloheximide. Furthermore, nanoceria had a stronger protective effect than trolox or NAC. Our findings also suggest that TNFα plus cycloheximide-induced apoptosis is dependent on alterations in cytosolic concentration of calcium [Ca²⁺]_c and ROS generation in human histiocytic U937 cells.     

Role of PKC-delta activity in glutathione-depleted neuroblastoma cells

Protein kinases C (PKCs) are a family of isoenzymes sensitive to oxidative modifications and involved in the transduction signal pathways that regulate cell growth. As such, they can act as cellular sensors able to intercept intracellular redox changes and promote the primary adaptive cell response. In this study, we have demonstrated that PKC isoforms are specifically influenced by the amount of intracellular glutathione (GSH). The greatest GSH depletion is associated with a maximal reactive oxygen species (ROS) production and accompanied by an increase in the activity of the delta isoform and a concomitant inactivation of alpha. ROS generation induced early morphological changes in GSH-depleted neuroblastoma cells characterized, at the intracellular level, by the modulation of PKC-delta activity that was involved in the pathway leading to apoptosis. When cells were pretreated with rottlerin, their survival was improved by the ability of this compound to inhibit the activity of PKC-delta and to counteract ROS production. These results define a novel role of PKC-delta in the cell signaling pathway triggered by GSH loss normally associated with many neurodegenerative diseases and clinically employed in the treatment of neuroblastoma.     

Intracellular glutathione depletion and reactive oxygen species generation are important in α-hederin-induced apoptosis of P388 cells

alpha-Hederin, a pentacyclic triterpene saponin isolated from the seeds of Nigella sativa, was recently reported to have potent in vivo antitumor activity against LL/2 (Lewis Lung carcinoma) in BDF1 mice. In this study we observed that alpha-hederin caused a dose- and time-dependent increase in apoptosis of murine leukemia P388 cells. In order to evaluate the possible mechanisms for apoptosis, the effects of alpha-hederin on intracellular thiol concentration, including reduced glutathione (GSH), and protein thiols, and the effects of pretreatment with N-acetlycysteine (NAC), a precursor of intracellular GSH synthesis, or buthionine sulfoxime (BSO), a specific inhibitor of intracellular GSH synthesis, on alpha-hederin-induced apoptosis were investigated. It was found that alpha-hederin rapidly depleted intracellular GSH and protein thiols prior to the occurrence of apoptosis. NAC significantly alleviated alpha-hederin-induced apoptosis, while BSO augmented alpha-hederin-induced apoptosis significantly. The depletion of cellular thiols observed after alpha-hederin treatment caused disruption of mitochondrial membrane potential (deltapsi(m)) and subsequently increased the production of reactive oxygen species (ROS) in P388 cells at an early time point. Bongkrekic acid (BA), a ligand of the mitochondrial adenine nucleotide translocator, and cyclosporin (CsA) attenuated the alpha-hederin-induced loss of deltapsi(m), and ROS production. Thus, oxidative stress after alpha-hederin treatment is an important event in alpha-hederin-induced apoptosis. As observed in this study, permeability transition of mitochondrial membrane occurs after depletion of GSH and precedes a state of reactive oxygen species (ROS) generation. Further, we observed that alpha-hederin caused the release of cytochrome c from the mitochondria to cytosol, leading to caspase-3 activation. Our findings thus demonstrate that changes in intracellular thiols and redox status leading to perturbance of mitochondrial functions are important components in the mechanism of alpha-hederin-induced cell death.     

Arachidonic acid converts the glutathione depletion-induced apoptosis to necrosis by promoting lipid peroxidation and reducing caspase-3 activity in rat glioma cells

Intracellular glutathione (GSH) depletion induced by buthionine sulfoximine (BSO) caused cell death that seemed to be apoptosis in C6 rat glioma cells. Arachidonic acid (AA) promoted BSO-induced cell death by accumulating reactive oxygen species (ROS) or hydroperoxides. AA inhibited caspase-3 activation and internucleosomal DNA fragmentation during the BSO-induced GSH depletion. Furthermore, AA reduced intracellular ATP content, induced dysfunction of mitochondrial membrane and enhanced 8-hydroxy-2'-deoxyguanosine (8-OH-dG) production. There was significant increase of 12-lipoxygenase activity in the presence of AA under the BSO-induced GSH depletion in C6 cells. These results suggest that AA promotes cell death by changing to necrosis from apoptosis through lipid peroxidation initiated by lipid hydroperoxides produced by 12-lipoxygenase under the GSH depletion in C6 cells. Some ROS such as hydroperoxide produced by unknown pathway make hydroxy radicals and induce 8-OH-dG formation in the cells. The conversion of apoptosis to necrosis may be a possible event under GSH depleted conditions.     

Suppression of arsenic trioxide-induced apoptosis in HeLa cells by N-acetylcysteine

Arsenic trioxide (ATO) can affect many biological functions such as apoptosis and differentiation in various cells. We investigated the involvement of ROS and GSH in ATO-induced HeLa cell death using ROS scavengers, especially N-acetylcysteine (NAC). ATO increased intracellular O(2)(*-) levels and reduced intracellular GSH content. The ROS scavengers, Tempol, Tiron and Trimetazidine, did not significantly reduce levels of ROS or GSH depletion in ATO-treated HeLa cells. Nor did they reduce the apoptosis induced by ATO. In contrast, treatment with NAC reduced ROS levels and GSH depletion in the ATO-treated HeLa cells and prevented ATO-induced apoptosis. Treatment with exogenous SOD and catalase reduced the depletion of GSH content in ATO-treated cells. Catalase strongly protected the cells from ATO-induced apoptosis. In addition, treatment with SOD, catalase and NAC slightly inhibited the G1 phase accumulation induced by ATO. In conclusion, NAC protects HeLa cells from apoptosis induced by ATO by up-regulating intracellular GSH content and partially reducing the production of O(2)(*-).     

GSH depletion, protein S-glutathionylation and mitochondrial transmembrane potential hyperpolarization are early events in initiation of cell death induced by a mixture of isothiazolinones in HL60 cells

We recently described that brief exposure of HL60 cells to a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) induces apoptosis at low concentrations (0.001-0.01%) and necrosis at higher concentrations (0.05-0.1%). In this study, we show that glutathione (GSH) depletion, reactive oxygen species generation, hyperpolarization of mitochondrial transmembrane potential (DeltaPsim) and formation of protein-GSH mixed disulphides (S-glutathionylation) are early molecular events that precede the induction of cell death by CMI/MI. When the cells exhibit common signs of apoptosis, they show activation of caspase-9, reduction of DeltaPsim and, more importantly, decreased protein S-glutathionylation. In contrast, necrosis is associated with severe mitochondrial damage and maximal protein S-glutathionylation. CMI/MI-induced cytotoxicity is also accompanied by decreased activity of GSH-related enzymes. Pre-incubation with L-buthionine-(S,R)-sulfoximine (BSO) clearly switches the mode of cell death from apoptosis to necrosis at 0.01% CMI/MI. Collectively, these results demonstrate that CMI/MI alters the redox status of HL60 cells, and the extent and kinetics of GSH depletion and S-glutathionylation appear to determine whether cells undergo apoptosis or necrosis. We hypothesize that S-glutathionylation of certain thiol groups accompanied by GSH depletion plays a critical role in the molecular mechanism of CMI/MI cytotoxicity.     

Thiol antioxidants protect human lens epithelial (HLE B-3) cells against tert-butyl hydroperoxide-induced oxidative damage and cytotoxicity

Oxidative damage to lens epithelial cells plays an important role in the development of age-related cataract, and the health of the lens has important implications for overall ocular health. As a result, there is a need for effective therapeutic agents that prevent oxidative damage to the lens. Thiol antioxidants such as tiopronin or N-(2-mercaptopropionyl)glycine (MPG), N-acetylcysteine amide (NACA), N-acetylcysteine (NAC), and exogenous glutathione (GSH) may be promising candidates for this purpose, but their ability to protect lens epithelial cells is not well understood. The effectiveness of these compounds was compared by exposing human lens epithelial cells (HLE B-3) to the chemical oxidant tert-butyl hydroperoxide (tBHP) and treating the cells with each of the antioxidant compounds. MTT cell viability, apoptosis, reactive oxygen species (ROS), and levels of intracellular GSH, the most important antioxidant in the lens, were measured after treatment. All four compounds provided some degree of protection against tBHP-induced oxidative stress and cytotoxicity. Cells treated with NACA exhibited the highest viability after exposure to tBHP, as well as decreased ROS and increased intracellular GSH. Exogenous GSH also preserved viability and increased intracellular GSH levels. MPG scavenged significant amounts of ROS, and NAC increased intracellular GSH levels. Our results suggest that both scavenging ROS and increasing GSH may be necessary for effective protection of lens epithelial cells. Further, the compounds tested may be useful for the development of therapeutic strategies that aim to prevent oxidative damage to the lens.     

Allicin inhibits cell growth and induces apoptosis through the mitochondrial pathway in HL60 and U937 cells

In this article, the effects of allicin, a biological active compound of garlic, on HL60 and U937 cell lines were examined. Allicin induced growth inhibition and elicited apoptotic events such as blebbing, mitochondrial membrane depolarization, cytochrome c release into the cytosol, activation of caspase 9 and caspase 3 and DNA fragmentation. Pretreatment of HL60 cells with cyclosporine A, an inhibitor of the mitochondrial permeability transition pore (mPTP), inhibited allicin-treated cell death. HL60 cell survival after 1 h pretreatment with cyclosporine A, followed by 16 h in presence of allicin (5 microM) was approximately 80% compared to allicin treatment alone (approximately 50%). Also N-acetyl cysteine, a reduced glutathione (GSH) precursor, prevented cell death. The effects of cyclosporine A and N-acetyl cysteine suggest the involvement of mPTP and intracellular GSH level in the cytotoxicity. Indeed, allicin depleted GSH in the cytosol and mitochondria, and buthionine sulfoximine, a specific inhibitor of GSH synthesis, significantly augmented allicin-induced apoptosis. In HL60 cells treated with allicin (5 microM, 30 min) the redox state for 2GSH/oxidized glutathione shifted from EGSH -240 to -170 mV. The same shift was observed in U937 cells treated with allicin at a higher concentration for a longer period of incubation (20 microM, 2 h). The apoptotic events induced by various concentrations of allicin correlate to intracellular GSH levels in the two cell types tested (HL60: 3.7 nmol/10(6) cells; U937: 7.7 nmol/10(6) cells). The emerging mechanistic basis for the antiproliferative function of allicin, therefore, involves the activation of the mitochondrial apoptotic pathway by GSH depletion and by changes in the intracellular redox status.     

Role of Oxidative Stress,Apoptosis, and Intracellular Homeostasis in Primary Cultures of Rat Proximal Tubular Cells Exposed to Cadmium

Cadmium (Cd) is a known nephrotoxic element. In this study, the primary cultures of rat proximal tubular (rPT) cells were treated with low doses of cadmium acetate (2.5 and 5 μM) to investigate its cytotoxic mechanism. A progressive loss in cell viability, together with a significant increase in the number of apoptotic and necrotic cells, were seen in the experiment. Simultaneously, elevation of intracellular [Ca²⁺]i and reactive oxygen species (ROS) levels, significant depletion of mitochondrial membrane potential(Δ Ψ) and cellular glutathione (GSH), intracellular acidification, and inhibition of Na⁺, K⁺-ATPase and Ca²⁺-ATPase activities were revealed in a dose-dependent manner during the exposure, while the cellular death and the apoptosis could be markedly reversed by N-acetyl-l-cysteine (NAC). Also, the calcium overload and GSH depletion were significantly affected by NAC. In conclusion, exposure of rPT cells to low-dose cadmium led to cellular death, mediated by an apoptotic and a necrotic mechanism. The apoptotic death might be the chief mechanism, which may be mediated by oxidative stress. Also, a disorder of intracellular homeostasis induced by oxidative stress and mitochondrial dysfunction is a trigger of apoptosis in rPT cells.     

Effects of naringin on cytosine arabinoside (Ara-C)-induced cytotoxicity and apoptosis in P388 cells

Naringin (NG), a flavonoid in grapefruit and citrus, has been reported to exhibit antioxidant effects and pharmacological actions. Recently, we have reported that NG suppressed the cytotoxicity and apoptosis induced by H(2)O(2), a typical pro-oxidant, in mouse leukemia P388 cells. Cytosine arabinoside (1-beta-d-arabinofuranosylcytosine; Ara-C) is the most important antimetabolite chemotherapeutic drug used for acute leukemia. It has been suggested that Ara-C-induced cytotoxicity is caused by apoptosis, which is mediated by reactive oxygen species (ROS). In this study, we examined the effect of NG on the cytotoxicity and apoptosis in mouse leukemia P388 cells treated with Ara-C. Ara-C caused cytotoxicity in a concentration and time-dependent manner in the cells. N-Acetyl-L-cysteine (NAC), cystamine (CysA) or a reduced form of glutathione (GSH), typical antioxidants significantly blocked Ara-C-induced cytotoxicity. Similarly, Ara-C-induced cell death was completely prevented by NG. NG strongly reduced ROS production caused by Ara-C in the cells. NG slightly increased the activities of antioxidant enzymes, catalase and glutathione peroxidase. Ara-C caused apoptosis with nuclear morphological change and DNA fragmentation. NG remarkably attenuated the Ara-C-induced apoptosis. NG completely blocked the DNA damage caused by Ara-C treatment at 6 h using the Comet assay. Our data suggest that NG reduces Ara-C-induced oxidative stress through both an inhibition of the generation of ROS production and an increase in antioxidant enzyme activities. Consequently, NG blocked apoptosis caused by Ara-C-induced oxidative stress, resulting in the inhibition of the cytotoxicity of Ara-C.     

The role of oxidative stress in the ochratoxin A-mediated toxicity in proximal tubular cells

Balkan endemic nephropathy (BEN), a disease characterized by progressive renal fibrosis in human patients, has been associated with exposure to ochratoxin A (OTA). This mycotoxin is a frequent contaminant of human and animal food products, and is toxic to all animal species tested. OTA predominantly affects the kidney and is known to accumulate in the proximal tubule (PT). The induction of oxidative stress is implicated in the toxicity of this mycotoxin.In the present study, primary rat PT cells and LLC-PK(1) cells, which express characteristics of the PT, were used to investigate the OTA-mediated oxidative stress response. OTA exposure of these cells resulted in a concentration-dependent elevation of reactive oxygen species (ROS) levels, depletion of cellular glutathione (GSH) levels and an increase in the formation of 8-oxoguanine.The OTA-induced ROS response was significantly reduced following treatment with alpha-tocopherol (TOCO). However, this chain-braking anti-oxidant did not reduce the cytotoxicity of OTA and was unable to prevent the depletion of total GSH levels in OTA-exposed cells. In contrast, pre-incubation of the cell with N-acetyl-L-cysteine (NAC) completely prevented the OTA-induced increase in ROS levels as well as the formation of 8-oxoguanine and completely protected against the cytotoxicity of OTA. In addition, NAC treatment also limited the GSH depletion in OTA-exposed PT- and LLC-PK(1) cells.From these data, we conclude that oxidative stress contributes to the tubular toxicity of OTA. Subsequently, cellular GSH levels play a pivotal role in limiting the short-term toxicity of this mycotoxin in renal tubular cells.