Protective Effects of Xanthine Derivatives Against Arsenic Trioxide-Induced Oxidative Stress in Mouse Hepatic and Renal Tissues.

In this study, the protective efficacy of pentoxifylline (PTX) as a xanthine derivative against arsenic trioxide (ATO)-induced kidney and liver damage in mice was investigated. Thirty-six mice were divided into six groups, receiving intraperitoneal injections of saline, ATO, PTX, or a combination for four weeks. Blood samples were analyzed for serum biochemistry, while hepatic tissue underwent examination for histopathological changes and assessment of oxidative stress markers and antioxidant gene expression through Real-Time PCR. ATO exposure significantly increased serum markers (creatinine, ALT, BUN, ALP, AST) and induced histopathological changes in the liver. Moreover, it elevated renal and hepatic nitric oxide (NO) and lipid peroxidation (LPO) levels, and reduced antioxidant enzyme expression (CAT, GSR, GPx, MPO, SOD), total thiol groups (TTGs), and total antioxidant capacity (TAC). Conversely, PTX treatment effectively lowered serum hepatic and renal markers, improved antioxidant markers, and induced histopathological alterations. Notably, PTX did not significantly affect renal and hepatic NO levels. These findings suggest that PTX offers therapeutic potential in mitigating liver and acute kidney injuries induced by various insults, including exposure to ATO.

AcGlcAs: A Novel P53-Targeting Arsenical with Potent Cellular Uptake and Cancer Cell Selectivity.

Arsenic trioxide (ATO) targets PML/RARα and leads to miraculous success in treating acute promyelocytic leukemia. Notably, ATO also targets p53, the most frequently mutated protein in cancers, through a similar binding mechanism. However, p53-targeting ATO trials are challenging due to the poor cellular uptake and cancer selectivity of ATO. Here, we analyzed the structure-activity relationship of arsenicals and rationally developed a novel arsenical (designated AcGlcAs) by conjugating arsenic to sulfur atoms and tetraacetyl-ß-d-thioglucose. AcGlcAs exhibited remarkable cellular uptake through a thiol-mediated pathway (maximally 127-fold higher than ATO), thereby potently targeting PML/RARα and mutant p53. Among the 55 tested cell lines, AcGlcAs preferentially killed cancer lines rather than normal lines. In preclinical studies, AcGlcAs significantly extended the survival of mice bearing a xenograft tumor with p53 mutation while showing high plasma stability and oral bioavailability. Thus, AcGlcAs is a potential clinical candidate for precisely treating numerous p53-mutated cancers.

Diverse rescue potencies of p53 mutations to ATO are predetermined by intrinsic mutational properties.

Tumor suppressor p53 is inactivated by thousands of heterogeneous mutations in cancer, but their individual druggability remains largely elusive. Here, we evaluated 800 common p53 mutants for their rescue potencies by the representative generic rescue compound arsenic trioxide (ATO) in terms of transactivation activity, cell growth inhibition, and mouse tumor-suppressive activities. The rescue potencies were mainly determined by the solvent accessibility of the mutated residue, a key factor determining whether a mutation is a structural one, and the temperature sensitivity, the ability to reassemble the wild-type DNA binding surface at a low temperature, of the mutant protein. A total of 390 p53 mutants were rescued to varying degrees and thus were termed as type 1, type 2a, and type 2b mutations, depending on the degree to which they were rescued. The 33 type 1 mutations were rescued to amounts comparable to the wild type. In PDX mouse trials, ATO preferentially inhibited growth of tumors harboring type 1 and type 2a mutants. In an ATO clinical trial, we report the first-in-human mutant p53 reactivation in a patient harboring the type 1 V272M mutant. In 47 cell lines derived from 10 cancer types, ATO preferentially and effectively rescued type 1 and type 2a mutants, supporting the broad applicability of ATO in rescuing mutant p53. Our study provides the scientific and clinical communities with a resource of the druggabilities of numerous p53 mutations (www.rescuep53.net) and proposes a conceptual p53-targeting strategy based on individual mutant alleles rather than mutation type.

Targeting HDAC3 to overcome the resistance to ATRA or arsenic in acute promyelocytic leukemia through ubiquitination and degradation of PML-RARα.

Acute promyelocytic leukemia (APL) is driven by the oncoprotein PML-RARα, which recruits corepressor complexes, including histone deacetylases (HDACs), to suppress cell differentiation and promote APL initiation. All-trans retinoic acid (ATRA) combined with arsenic trioxide (ATO) or chemotherapy highly improves the prognosis of APL patients. However, refractoriness to ATRA and ATO may occur, which leads to relapsed disease in a group of patients. Here, we report that HDAC3 was highly expressed in the APL subtype of AML, and the protein level of HDAC3 was positively associated with PML-RARα. Mechanistically, we found that HDAC3 deacetylated PML-RARα at lysine 394, which reduced PIAS1-mediated PML-RARα SUMOylation and subsequent RNF4-induced ubiquitylation. HDAC3 inhibition promoted PML-RARα ubiquitylation and degradation and reduced the expression of PML-RARα in both wild-type and ATRA- or ATO-resistant APL cells. Furthermore, genetic or pharmacological inhibition of HDAC3 induced differentiation, apoptosis, and decreased cellular self-renewal of APL cells, including primary leukemia cells from patients with resistant APL. Using both cell line- and patient-derived xenograft models, we demonstrated that treatment with an HDAC3 inhibitor or combination of ATRA/ATO reduced APL progression. In conclusion, our study identifies the role of HDAC3 as a positive regulator of the PML-RARα oncoprotein by deacetylating PML-RARα and suggests that targeting HDAC3 could be a promising strategy to treat relapsed/refractory APL.

Arsenic trioxide sensitizes pancreatic cancer cells to gemcitabine through downregulation of the TIMP1/PI3K/AKT/mTOR axis.

Gemcitabine (GEM) is the first-line medication for pancreatic ductal adenocarcinoma (PDAC). However, over some treatment cycles, GEM sensitivity declines and chemotherapeutic resistance develops, resulting in tumor recurrence and metastasis. Therefore, it is critical to elucidate the mechanism of GEM chemoresistance. And a specific drug that is closely related to the mechanism is urgently required to sensitize GEM. Here, tissue inhibitor of matrix metalloproteinases 1 (TIMP1) and phosphorylated mammalian target of rapamycin (p-mTOR) were found to be substantially elevated in PDAC patients and were associated with worse overall survival. The TIMP1/PI3K/AKT/mTOR pathway was found in GEM-resistant PDAC cells and was revealed to be involved in epithelial-mesenchymal transition (EMT) and apoptosis. Furthermore, arsenic trioxide (ATO), a basic therapeutic drug for acute promyelocytic leukemia, mediated TIMP1 reduction by inducing reactive oxygen species generation and hampered the subsequent PI3K/AKT/mTOR axis. Moreover, the combination of ATO and GEM cooperatively suppressed the TIMP1/PI3K/AKT/mTOR pathway, synergistically inhibited EMT and promoted apoptosis. In vitro and in vivo, ATO combined with GEM has a collaborative anticancer effect, inhibiting cancer cell proliferation, migration, invasion, and suppressing tumor growth both in PDAC parental and GEM-resistant cells. Overall, the TIMP1/PI3K/AKT/mTOR pathway is present in PDAC and linked to GEM resistance. ATO suppresses the axis to sensitize GEM and reverse GEM resistance, suggesting a promising treatment for the disease.

[CircRNA-0028171 regulates arsenic trioxide-induced apoptosis in vascular endothelial cells].

The present study was aimed to investigate the effects of circRNA-0028171 on the apoptosis of vascular endothelial cells induced by arsenic trioxide (As2O3). Human umbilical vein endothelial cells (HUVECs) were treated with 0-15 µmol/L As2O3 for 24 h. Then, cellular viability was measured by MTT assay. The expression levels of circRNA-0028171, Bcl-2 and Bax mRNA were detected by real-time quantitative PCR. Bcl-2/Bax protein ratio was detected by Western blot. Whether circRNA-0028171 was involved in the regulation of HUVECs by As2O3 was investigated by transfection with overexpression plasmid of circRNA-0028171 and siRNA. The results showed that compared with the control group, As2O3 group showed decreased cellular viability, reduced Bcl-2/Bax mRNA and protein ratios, and significantly lower expression of circRNA-0028171. Overexpression of circRNA-0028171 inhibited apoptosis of HUVECs induced by As2O3. Knockdown of circRNA-0028171 by siRNA promoted As2O3-induced apoptosis in HUVECs. These results suggest that circRNA-0028171 is involved in the vascular endothelial cell apoptosis induced by As2O3.

Mitochondrial Toxicity of Organic Arsenicals.

Arsenic is either notorious toxicant or miracle cure for acute promyelocytic leukemia and several other diseases. It interacts with mitochondria directly or indirectly, by interacting with mitochondrial enzymes, such as respiratory chain complexes and tricarboxylic acid cycle proteins, or affecting mitochondrial homeostasis via ROS or mitochondrial outer membrane permeabilization. Given the ubiquitous presence of mitochondria and indispensable role in cellular metabolism, arsenical-mitochondrial interactions may manifest clinical importance by revealing mechanism of disease curation, preventing severe side effects, and foreseeing potential health issues. Here, we described the interaction between isolated mitochondria and arsenicals.

Low-dose arsenic trioxide enhances membrane-GLUT1 expression and glucose uptake via AKT activation to support L-02 cell aberrant proliferation.

Long term low dose exposure of arsenic has been reported to lead various cells proliferation and malignant transformation. GLUT1, as the key transporter of glucose, has been reported to have association with rapid proliferation of various cells or tumor cells. In our study, we found that low dose exposure to arsenic trioxide (0.1µmol/L As2O3) could induce an increase in glucose uptake and promote cell viability and DNA synthesis. And, 2-DG, a non-metabolized glucose analog, significantly decreased the glucose uptake and cell proliferation of 0.1µmol/L As2O3 treated L-02 cells. However, 4 mmol/L 2-DG was co-utilized with equal dose glucose had no significant effect on the cell proliferation of 0.1µmol/L As2O3 treated L-02 cells. Further studies showed that exposure to 0.1µmol/L As2O3 could promote the expression of GLUT1 on plasma membrane. Inhibition of GLUT1 expression by 5µmol/L BAY-876 significantly decreased the abilities of glucose uptake and cell proliferation in As2O3-treated L-02 cells. Moreover, 0.1µmol/L As2O3 induced the AKT activation indicated by increased the phospho-AKT (Ser473 and Thr308). Knockdown AKT by shRNA or inhibited AKT activation by LY294002 was followed by significantly decreased glucose uptake, GLUT1 plasma membrane expression and cell proliferation in As2O3-treated L-02 cells. All in all, these results demonstrated that arsenic trioxide-induced AKT activation contributed to the cells proliferation through upregulating expression of GLUT1 on plasma membrane that enhanced glucose uptake.

Arsenic trioxide induces the differentiation of retinoic acid-resistant neuroblastoma cells via upregulation of HoxC9.

BACKGROUND: Neuroblastoma (NB) is one of the most common extracranial tumors with limited therapeutic options. Retinoic acid (RA) has been identified to play anticancer role against NB cells by inducing the differentiation and apoptosis of immature neuroblasts. However, silencing HoxC9 promoter by EZH2-induced H3K27me3 hypermethylation can lead to RA resistance. Previous studies have suggested that arsenic trioxide (ATO), an inhibitor of DNA methylation, could downregulate the expression of EZH2 in breast cancer cells. OBJECTIVES: In our study, we attempted to obtain some insight into the mechanisms of differentiation of RA-resistant NB cells by detecting the expressions of HoxC9 and EZH2 in NB cells treated with ATO, so as to provide a basis for the subsequent treatment of RA-resistant NB by ATO. MATERIAL AND METHODS: Two NB cell lines, SK-N-AS (retinoic acid-resistant neuroblastoma cells) and SK-N-SH (retinoic acid-sensitive neuroblastoma cells), were used in our experiments. Cell proliferation and apoptosis were respectively determined with Cell Counting Kit-8 (CCK-8) assay kit and Annexin V staining. The inverted phase contrast microscope was used to observe cell growth and measure the total length of nerve synapses. We employed label-free quantitative proteomic analysis to profile ATO-dependent changes in the proteome of NB cells. Western blot was used to detect the expressions of HoxC9, HoxD8 and EZH2. RESULTS: Arsenic trioxide inhibited the cell proliferation and increased apoptosis and total length of synapses in two NB cell lines. The expressions of HoxC9 and HoxD8 were upregulated, while the expression of EZH2 was downregulated in the SK-N-AS cell line. No significant changes in the 3 proteins mentioned above were observed in the SK-N-SH cell line after ATO treatment. CONCLUSIONS: Arsenic trioxide may reactivate the expression of HoxC9 by downregulating EZH2, which leads to restoring RA sensitivity and promoting the differentiation and apoptosis of RA-resistant NB cells.

Human prostate cancer cell epithelial-to-mesenchymal transition as a novel target of arsenic trioxide and curcumin therapeutic approach.

BACKGROUND: Arsenic trioxide (As2O3) as an inorganic compound is used to treat various cancers and other diseases. It has been reported that arsenic trioxide induced cellular apoptosis in certain kinds of cancers, including prostate cancers. The present study aimed to elucidate the crucial cooperative role of arsenic trioxide and Curcumin and their ability to protect against prostate cancers by targeting the epithelial-to-mesenchymal transition and expression of apoptosis-related genes. MATERIAL AND METHODS: The human prostate cell lines (LNCaP and PC3) were treated with different concentrations of Curcumin and As2O3 alone and combined to find effective doses and IC50 values. Percentages of apoptotic cells were evaluated by Annexin/P.I. staining, the proliferative inhibitory effect was assessed by Micro Culture Tetrazolium Test (MTT), and mRNA levels of KLK2, E-cadherin, SNAIL, angiogenesis genes (VEGFA and VEGFC), and apoptosis genes (BAX, Bcl2, and P53) expression were investigated by the real-time PCR method. ANOVA and t-test were used to appraise the results. RESULTS: For the first time, we presented that the combination therapy of Curcumin and As2O3 increases prostate cancer cell apoptosis and inhibits proliferation; Our data displayed that Curcumin (15 µM and 10 µM in PC3 and LNCap), As2O3 (8 µM and 5 µM in PC3 and LNCap), and also their combination (15 µM Curcumin and 8 µM As2O3 in PC3, 10 µM Curcumin and 5 µM As2O3 in LNCap cell lines) significantly increased the percentage of apoptotic cells and inhibited cell growth (P < 0.05) compared with each drug alone. Generally, both cell lines treated with the combination of Curcumin and As2O3 displayed decreased angiogenesis genes (VEGFA and VEGFC), apoptosis genes (BAX and Bcl2), and prostate cancer marker (KLK2), the zinc-finger protein (SNAIL); and an increase in expression (P < 0.05) of cell-cell adhesion molecule (E-cadherin) and tumor suppressor gene (P53) genes. CONCLUSIONS: The antitumor effects of combination therapy with As2O3 and Curcumin have been displayed on prostate cancer cell lines (LNCaP and PC3), which probably originates from their potential to induce apoptosis and inhibit the growth of prostate cancer cells simultaneously.

The Oxidative Drug Combination for Suppressing KRAS G12D Inducible Tumour Growth.

Background: Kirsten rat sarcoma (KRAS) protein is an essential contributor to the development of pancreatic ductal adenocarcinoma (PDAC). KRAS G12D and G12V mutant tumours are significant challenges in cancer therapy due to high resistance to the treatment. Objective: To determine how effective is the ATO/D-VC combination in suppression of PDAC the mouse transgenic model. This study investigated the antitumour effect of a novel combination of arsenic trioxide (ATO) and D-ascorbic acid isomer (D-VC). Such a combination can be used to treat KRAS mutant cancer by inducing catastrophic oxidative stress. Methods: In this study, we examined the effectiveness of ATO and D-VC on xenograft models-AK192 cells transplanted into mice. Previously, it has been shown that a high concentration of Vitamin C (VC) selectively can kill the cells expressing KRAS. Results: The results of this study demonstrated that the combination of VC with a low dose of the oxidizing drug ATO led to the enhancement of the therapeutic effect. These findings suggest that the combined treatment using ATO and D-VC is a promising approach to overcome the limitation of drug selectivity and efficacy.

Polymorphisms of the AS3MT gene are associated with arsenic methylation capacity and damage to the P21 gene in arsenic trioxide plant workers.

Epidemiological evidence suggests that the metabolic profiles of each individual exposed to arsenic (As) are related to the risk of cancer, coronary heart disease, and diabetes. The arsenite methyltransferase (AS3MT) gene plays a key role in As metabolism. Several single nucleotide polymorphisms in the AS3MT gene may affect both enzyme activity and gene transcription. AS3MT polymorphisms are associated with the proportions of monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA) in urine as well as the incidence of cancer. P21 protein is a cyclin-dependent kinase inhibitor. Mutations of the P21 gene have been found in cancer patients. In our study, we investigate whether polymorphisms of the AS3MT gene alter As methylation capacity and adversely affect the P21 gene in arsenic trioxide plant workers. The DNA damage was examined by the quantitative polymerase chain reaction. Restriction fragment length polymorphism was used to analyze the genotype of the AS3MT gene. The results showed that DNA damage in P21 gene fragments was greater in those individuals exposed to high levels of As. There was a strong positive correlation between the DNA damage to P21 gene fragments and the percentage of MMA in urine. However, DNA damage in P21 gene fragments was negatively associated with the percentage of DMA in urine (%uDMA), primary methylation index (PMI), and secondary methylation index. We found that subjects with the rs7085104 GG or GA allele were associated with higher %uDMA and PMI and less DNA damage. The subjects with the rs11191454 GG+GA or GA allele were also associated with higher %uDMA and PMI and less DNA damage. Our results suggest that rs1191454 and rs7085104 in the AS3MT gene affect the As-induced DNA damage by altering individual metabolic efficiency.

Investigation of the Physical Properties and Clinical Application of Embosphere Microspheres.

BACKGROUND: The aim of this study was to understand physical characteristics of Embosphere microspheres for the clinical use of microsphere chemotherapy embolization of liver cancer. METHODS: The morphology of Embosphere microspheres in different states, including static, oscillating, and in a magnetic field was observed with the naked eye. Ninety-five patients diagnosed with primary hepatocellular carcinoma (HCC) were separated into 3 groups based on the types of embolic material as follows: 32 cases of sole microspheres, 34 cases of iodinated oil (17 cases with additional application of gelatin sponge particle), and 29 cases of iodinated oil + Embosphere microspheres. RESULTS: The diameter of the microspheres ranged from 100 to 300 µm, with a sedimentation rate υ = 0.0375 cm/s in physiological saline. The diameter of microspheres ranged from 300 to 500 µm, with a sedimentation rate υ = 0.1875 cm/s. The swelling rate of microspheres was 90%. Microspheres showed nondirectional movement in a 1.5- or 3.0-T magnetic field during magnetic resonance imaging. A volumetric ratio of 1:1.4-1:1.5 between microspheres and contrast agent resulted in optimal suspension properties. Microspheres appeared circular with a smooth surface upon water adsorption. Microsphere embolism was observable in blood vessels of pathological sections. The surface of microspheres can adsorb 5-fluorouracil and arsenic trioxide. There are statistically significant differences in local-regional tumor control conditions among patients treated with sole microspheres, iodinated oil, and iodinated oil + microspheres during transarterial chemoembolization. CONCLUSIONS: Embosphere microspheres can be used to embolize patients with rupture and hemorrhage of HCC. Embosphere microsphere embolization is superior to iodinated oil and iodinated oil + microsphere for HCC.

Crosstalk between hnRNP K and SET in ATRA-induced differentiation in acute promyelocytic leukemia.

HnRNP K protein is a heterogeneous nuclear ribonucleoprotein which has been proposed to be involved in the leukemogenesis of acute promyelocytic leukemia (APL), as well as in differentiation induced by all-trans retinoic acid (ATRA). We previously demonstrated a connection between SET and hnRNP K function in head and neck squamous cell carcinoma (HNSCC) cells related to splicing processing. The objective of this study was to characterize the participation of hnRNP K and SET proteins in ATRA-induced differentiation in APL. We observed higher (5- to 40-fold) levels of hnRNP K and SET mRNA in APL patients at the diagnosis phase compared with induction and maintenance phases. hnRNP K knockdown using short-hairpin RNA led to cell death in ATRA-sensitive NB4 and resistant NB4-R2 cells by apoptosis with SET cleavage. In addition, hnRNP K knockdown increased granulocytic differentiation in APL cells, mainly in NB4-R2 with ATRA. hnRNP K knockdown had an effect similar to that of treatment with U0126 (an meiosis-specific serine/threonine protein kinase/ERK inhibitor), mainly in NB4-R2 cells. SET knockdown in APL cells revealed that apoptosis induction in cells with hnRNP K knockdown occurred by SET cleavage rather than by reduction in SET protein. Transplantation of NB4-R2 cells into nude mice confirmed that arsenic trioxide (ATO) combined with U0126 has higher potential against tumor progression when compared to ATO. Therefore, hnRNP K/SET and ERK are potential therapeutic targets for both antineoplastic leukemia therapy and relapsed APL patients with ATRA resistance.

Arsenic hexoxide has differential effects on cell proliferation and genome-wide gene expression in human primary mammary epithelial and MCF7 cells.

Arsenic is reportedly a biphasic inorganic compound for its toxicity and anticancer effects in humans. Recent studies have shown that certain arsenic compounds including arsenic hexoxide (AS4O6; hereafter, AS6) induce programmed cell death and cell cycle arrest in human cancer cells and murine cancer models. However, the mechanisms by which AS6 suppresses cancer cells are incompletely understood. In this study, we report the mechanisms of AS6 through transcriptome analyses. In particular, the cytotoxicity and global gene expression regulation by AS6 were compared in human normal and cancer breast epithelial cells. Using RNA-sequencing and bioinformatics analyses, differentially expressed genes in significantly affected biological pathways in these cell types were validated by real-time quantitative polymerase chain reaction and immunoblotting assays. Our data show markedly differential effects of AS6 on cytotoxicity and gene expression in human mammary epithelial normal cells (HUMEC) and Michigan Cancer Foundation 7 (MCF7), a human mammary epithelial cancer cell line. AS6 selectively arrests cell growth and induces cell death in MCF7 cells without affecting the growth of HUMEC in a dose-dependent manner. AS6 alters the transcription of a large number of genes in MCF7 cells, but much fewer genes in HUMEC. Importantly, we found that the cell proliferation, cell cycle, and DNA repair pathways are significantly suppressed whereas cellular stress response and apoptotic pathways increase in AS6-treated MCF7 cells. Together, we provide the first evidence of differential effects of AS6 on normal and cancerous breast epithelial cells, suggesting that AS6 at moderate concentrations induces cell cycle arrest and apoptosis through modulating genome-wide gene expression, leading to compromised DNA repair and increased genome instability selectively in human breast cancer cells.

Different mechanisms of arsenic related signaling in cellular proliferation, apoptosis and neo-plastic transformation.

Arsenic is a toxic heavy metal vastly dispersed all over the earth crust. It manifests several major adverse health issues to millions of arsenic exposed populations. Arsenic is associated with different types of cancer, cardiovascular disorders, diabetes, hypertension and many other diseases. On the contrary, arsenic (arsenic trioxide, As2O3) is used as a chemotherapeutic agent in the treatment of acute promyelocytic leukemia. Balance between arsenic induced cellular proliferations and apoptosis finally decide the outcome of its transformation rate. Arsenic propagates signals via cellular and nuclear pathways depending upon the chemical nature, and metabolic-fates of the arsenical compounds. Arsenic toxicity is propagated via ROS induced stress to DNA-repair mechanism and mitochondrial stability in the cell. ROS induced alteration in p53 regulation and some mitogen/ oncogenic functions determine the transformation outcome influencing cyclin-cdk complexes. Growth factor regulator proteins such as c-Jun, c-fos and c-myc are influenced by chronic arsenic exposure. In this review we have delineated arsenic induced ROS regulations of epidermal growth factor receptor (EGFR), NF-ĸß, MAP kinase, matrix-metalloproteinases (MMPs). The role of these signaling molecules has been discussed in relation to cellular apoptosis, cellular proliferation and neoplastic transformation. The arsenic stimulated pathways which help in proliferation and neoplastic transformation ultimately resulted in cancer manifestation whereas apoptotic pathways inhibited carcinogenesis. Therapeutic strategies against arsenic should be designed taking into account all these factors.

Role of cofilin­1 in arsenic trioxide­induced apoptosis of NB4­R1 cells.

All­trans retinoic acid (ATRA) and arsenic trioxide (As2O3) are currently first­line treatments for acute promyelocytic leukemia (APL). However, a number of patients with APL are resistant to ATRA but still sensitive to As2O3, and the underlying mechanisms of this remain unclear. In the present study, two­dimensional gel electrophoresis, mass spectrometry and other proteomic methods were applied to screen and identify the differentially expressed proteins between the retinoic acid­sensitive cell lines and drug­resistant cell lines. The results demonstrated that in retinoic acid­resistant NB4­R1 cells, the protein expression of cofilin­1 was markedly increased compared with that in the drug­sensitive NB4 cells. Subsequently, the effects of cofilin­1 on As2O3­induced apoptosis in NB4­R1 cells were further investigated. The results revealed that cell viability was markedly suppressed and apoptosis was increased in the As2O3­treated NB4­R1 cells, with increased expression levels of cleaved­poly (ADP­ribose) polymerase and cleaved­caspase 12. Cofilin­1 expression was significantly decreased at both the mRNA and protein levels in the As2O3­treated group compared with the control. Western blotting further revealed that As2O3 treatment decreased the cytoplasmic cofilin­1 level but increased its expression in the mitochondrion. However, the opposite effects of As2O3 on the cytochrome C distribution were found in NB4­R1 cells. This suggested that As2O3 can induce the transfer of cofilin­1 from the cytoplasm to mitochondria and trigger the release of mitochondrial cytochrome C in NB4­R1 cells. Moreover, cofilin­1 knockdown by its specific short hairpin RNA significantly suppressed As2O3­induced NB4­R1 cell apoptosis and inhibited the release of mitochondrial cytochrome C. Whereas, overexpression of cofilin­1 using a plasmid vector carrying cofilin­1 increased the release of cytochrome C into the cytoplasm from the mitochondria in As2O3­treated NB4­R1 cells. In conclusion, cofilin­1 played a role in As2O3­induced NB4­R1 cell apoptosis and it might be a novel target for APL treatment.

Biotransformation of arsenic and toxicological implication of arsenic metabolites.

Arsenic is a well-known environmental carcinogen and chronic exposure to arsenic through drinking water has been reported to cause skin, bladder and lung cancers, with arsenic metabolites being implicated in the pathogenesis. In contrast, arsenic trioxide (As2O3) is an effective therapeutic agent for the treatment of acute promyelocytic leukemia, in which the binding of arsenite (iAsIII) to promyelocytic leukemia (PML) protein is the proposed initial step. These findings on the two-edged sword characteristics of arsenic suggest that after entry into cells, arsenic reaches the nucleus and triggers various nuclear events. Arsenic is reduced, conjugated with glutathione, and methylated in the cytosol. These biotransformations, including the production of reactive metabolic intermediates, appear to determine the intracellular dynamics, target organs, and biological functions of arsenic.

Cytotoxic and genotoxic effects of arsenic on erythrocytes of Oryzias latipes: Bioremediation using Spirulina platensis.

BACKGROUND: Exposure to the environmental pollutants poses a serious threat to aquatic organism. The arsenic exposure in fish increases the risk of developing serious alterations from embryo to adult. OBJECTIVES: The present investigation was done to study the toxic effects of heavy metal arsenic [As(III)] on medaka (Oryzias latipes). Morphological alterations, apoptosis, nuclear abnormalities, and genotoxic biomarkers in erythrocytes were used to determine the stress caused by arsenic (As) exposure. METHODS: Medaka was exposed to As for 15 days at two toxic sublethal concentrations (7 ppm and 10 ppm) in combination with Spirulina platensis (SP) treatment as antioxidant algae at 200 mg/L. RESULTS: Results were consistent with a previous study results on tilapia. Exposure of medaka to As resulted in a dose-dependent increase in most the biomarkers used in the current study. Fish exposed to10 ppm As showed highest level of DNA damage. For the first time to our knowledge, using SP to counter the As toxicity in medaka, DNA damage restored to control levels. CONCLUSION: Accordingly, those results suggests that SP can protect medaka in aquaculture against As-induced damage by its ability as reactive oxygen species (ROS) reducer, antioxidant role, and DNA damage scavenger.

Effects of Proanthocyanidins on Arsenic Methylation Metabolism and Efflux in Human Hepatocytes L-02.

This study investigated the effects of proanthocyanidins (PC) on arsenic methylation metabolism and efflux in human hepatocytes (L-02), as well as the relationships between PC and GSH, MRP1 and other molecules. Cells were randomly divided into blank control group, arsenic trioxide exposure group (ATO, As2O3, 25µmol/L), and PC-treated arsenic exposure group (10, 25, 50mg/L). After 24/48h, the contents of different forms of arsenic were determined, and the methylation indexes were calculated. Intracellular S-adenosyl methionine (SAM), arsenic (+3 oxidation state) methyltransferase (AS3MT), multidrug resistance-associated protein 1 (MRP1), and reduced glutathione (GSH) were ascertained. Changing trends were observed and the correlation between arsenic metabolism and efflux related factors and arsenic metabolites was analyzed. We observed that cells showed increased levels of content/constituent ratio of methyl arsenic, primary/secondary methylation index, methylation growth efficiency/rate, and the difference of methyl arsenic content in cells and culture medium (P<0.05, resp.). Compared with ATO exposure group, the intracellular SAM content in PC-treated group decreased, and the contents of GSH, AS3MT, and MRP1 increased (P<0.05, resp.). There was a positive correlation between the content of intracellular GSH/AS3MT and methyl arsenic. The content of MRP1 was positively correlated with the difference of methyl arsenic content in cell and culture medium; conversely, the SAM content was negatively correlated with intracellular methyl arsenic content (P<0.05, resp.). Taken together, these results prove that PC can promote arsenic methylation metabolism and efflux in L-02 cells, which may be related to the upregulation of GSH, MRP1, and AS3MT levels by PC.