Metabolic control by dehydroascorbic acid: Questions and controversies in cancer cells

For a long time, the effect of vitamin C on cancer cells has been a controversial concept. From Linus Pauling's studies in 1976, it was proposed that ascorbic acid (AA) could selectively kill tumor cells. However, further research suggested that vitamin C has no effect on tumor survival. In the last decade, new and emerging functions for vitamin C have been discovered using the reduced form, AA, and the oxidized form, dehydroascorbic acid (DHA), independently. In this review, we summarized the latest findings related to the effects of DHA on the survival and metabolism of tumor cells. At the same time, we put special emphasis on the bystander effect and the recycling capacity of vitamin C in various cellular models, and how these concepts can affect the experimentation with vitamin C and its therapeutic application in the treatment against cancer.     

Mechanisms of vitamin C stabilization by K562 erythroleukemic cells

Summary K562 cells display several possibilities to keep ascorbic acid in the surrounding medium in the reduced state and prevent its loss by degradation of the oxidized form, dehydroascorbic acid: (1) A semidehydroascorbic acid reductase with high affinity for the ascorbate radical scavenges this before it disproportionates into the two parent forms of vitamin C (ascorbate and dehydroascorbic acid). (2) Dehydroascorbic acid in the extracellular medium is slowly converted to ascorbate by a different mechanism with low affinity which may or may not involve uptake of the oxidized and release of the reduced form. (3) Ascorbate remains relatively stable in the cell culture medium in presence, but also in absence of the cells after their removal, This is most probably due to the presence of released peptides in the cell-conditioned medium which can chelate transition metal ions and thus prevent catalytic autoxidation of ascorbate.     

Ascorbate synthesis and ascorbate peroxidase activity during the early stage of wheat germination

Embryos from dry caryopses of wheat ( Triticum durum L. cv. Norba) are completely devoid of ascorbate (ASC) but contain a low amount of dehydroascorbate (DHA). The de novo biosynthesis of ASC starts in the wheat embryos after 8–10 h of germination but before the ASC biosynthetic pathway is completely restored the embryos can provide themselves with ASC by the reduction of the stored DHA. Three different proteins having DHA-reducing capability are present in the embryos during the early stages of germination. However, when the de novo ASC biosynthesis from sugar is completely restored, the DHA reduction capability largely drops and only one DHA-reducing protein remains active. The presence of three proteins having DHA-reducing capability and their behaviour during germination is discussed.
Dry embryos are also devoid of ASC peroxidase (EC 1.11.1.11); this hydrogen peroxide scavenger enzyme appears after the same lag as ASC and increases during germination in parallel with the rise in ASC. When ASC biosynthesis is experimentally induced, the ASC peroxidase also appears earlier; moreover the affinities for ASC of the three ASC peroxidase isoenzymes that progressively appear during germination depend on the ASC available in the embryos: highest in the first isoenzyme, that appears when the ASC content is very low, lowest in the isoenzyme that is expressed last, when the ASC content is 10–11 times higher.     

Stereoselective Accumulation of Propranolol Enantiomers in K562 and K562/ADR Cells

The stereoselective uptake of propranolol enantiomers was investigated by using the K562 and K562 adriamycin‐resistant cell line (K562/ADR) as a model. An enantioselective RP‐HPLC method was applied to determine the accumulation of propranolol (PPL) stereoisomers in K562 and K562/ADR cells. The concentration, time and temperature dependent studies showed that the accumulation of S‐(?)‐PPL was higher than R‐(+)‐PPL in K562 cells and uptake of R‐(+)‐PPL was significantly higher than that of S‐(?)‐PPL in K562/ADR cells. The results indicate the enantioselective accumulation of propranolol enantiomers in K562 and K562 / ADR cells. Chirality 25:361–364, 2013. © 2013 Wiley Periodicals, Inc.     

Humanin delays apoptosis in K562 cells by downregulation of P38 MAP kinase

Humanin (HN) is a newly identified neuroprotective peptide. In this study, we investigated its antiapoptotic effect and the potential mechanisms in K562 cells. Upon serum deprivation, expression of HN in K562 cells decreased and its intracellular distribution changed from cytoplasm to cell membrane. In HN stably transfected K562 cells, apoptosis was delayed compared with control vector transfected cells as measured by flow cytometry. Furthermore, analysis of different mitogen-activated protein (MAP) kinases activity revealed that extracellular signal-regulated kinase (ERK) pathway was inhibited while p38 signaling was activated following serum deprivation in K562 cells. And in HN transfected K562 cells, ERK downregulation was not affected, but p38 activation was suppressed, which may responsible for the delayed apoptosis in these cells. Activation of the ERK signaling pathway by phorbol myristate 13-acetate (PMA) and sorbitol protected K562 cells from serum deprivation induced apoptosis. Additionally, overexpression of HN reduced megakaryocytic differentiation of K562 cells. The present data outline the role of ERK and p38 MAP kinases in serum deprivation induced apoptosis in K562 cells and figure out p38 signaling pathway as molecular target for HN delaying apoptosis in K562 cells.     

Adriamycin resistance is characterized by ultrastructural changes in human leukaemic K562 cells in vitro.

Ultrastructural changes associated with adriamycin (ADM) resistance have been investigated in the human K562 leukaemic cell line: sensitive K562 cells, a resistant subline cultured in the continuous presence of ADM and resistant cells without ADM Transmission electron microscopy (TEM) study revealed that K562-resistant cells displayed ultrastructural modifications of the cell surface, chromatin and nucleolus conformation. Alterations were not directly related to the presence of adriamycin as deprivated cells exhibited modificated characters through a slow progressive recovery phenomenon.     

Quercetin prevents glutathione depletion induced by dehydroascorbic acid in rabbit red blood cells

Exposure of rabbit red blood cells to dehydroascorbic acid (DHA) caused a significant decline in glutathione content which was largely prevented by quercetin, whereas it was insensitive to various antioxidants, iron chelators or scavengers of reactive oxygen species. This response was not mediated by chemical reduction of either extracellular DHA or intracellular glutathione disulfide. In addition, the flavonoid did not affect the uptake of DHA or its reduction to ascorbic acid. Rather, quercetin appeared to specifically stimulate downstream events promoting GSH formation.     

Reduction of dehydroascorbic acid at low pH

Ascorbic acid and dehydroascorbic acid are unstable in aqueous solution in the presence of copper and iron ions, causing problems in the routine analysis of vitamin C. Their stability can be improved by lowering the pH below 2, preferably with metaphosphoric acid. Dehydroascorbic acid, an oxidised form of vitamin C, gives a relatively low response on the majority of chromatographic detectors, and is therefore routinely determined as the increase of ascorbic acid formed after reduction. The reduction step is routinely performed at a pH that is suboptimal for the stability of both forms. In this paper, the reduction of dehydroascorbic acid with tris-[2-carboxyethyl] phosphine (TCEP) at pH below 2 is evaluated. Dehydroascorbic acid is fully reduced with TCEP in metaphosphoric acid in less than 20 min, and yields of ascorbic acid are the same as at higher pH. TCEP and ascorbic acid formed by reduction, are more stable in metaphosphoric acid than in acetate or citrate buffers at pH 5, in the presence of redox active copper ions. The simple experimental procedure and low probability of artefacts are major benefits of this method, over those currently applied in a routine assay of vitamin C, performed on large number of samples.     

Pattern expression of glycan residues in AZT-treated K562 cells analyzed by lectin cytochemistry

The present paper shows that human chronic myeloid (K562) cells exposed 3 h to 20 μM 3′-azido-3′-deoxythymidine (AZT) exhibit marked variations of the oligosaccharide moiety of glycoconjugates. These changes were analyzed by confocal fluorescence microscopy, upon incubation of control and AZT-treated cells with biotin–lectin conjugates to visualize cell surface glycans or total glycans after cells permeabilization. In addition, cell fluorescence distribution of the biotinylated lectins, localized with streptavidin conjugates labeled with Alexa Fluor 488, was analyzed by flow cytometry. The results obtained show significant variations on the expression/distribution of membrane surface glycans as detected by both WGA and SNA, two lectins that recognize primarily cellular internal membrane glycolipids. A further interesting result was the significant increase of N-acetylglucosamine linked glycans localized either at the cell surface or intracellularly but only in K562 cells exposed to AZT. On the whole, our data demonstrate that AZT alters both lipid and N-linked glycosylations thus confirming previous observations, from our laboratory and from other Authors, that the drug impair the nucleotide-sugar import in the Golgi’s lumen. AZT does also alter the O-linked glycosylations that occur in the Golgi complex since these reactions require the incorporation of sialic acid, GlcNAc and GalNAc all of which are sensitive to the drug.     

Dehydroascorbic Acid Reduction in Several Tissues and Cultured Hepatocytes of the Chicken

Dehydroascorbic acid, the oxidized form of ascorbic acid, is rapidly reduced to ascorbate in living organs (ascorbate recycling). We examined the GSH-dependent dehydroascorbate reductase activity in several tissues of the chicken. The activity was highest in the liver, and second highest in the brain. The activity was localized in the cytosol fraction of the liver. We subsequently examined the dehydroascorbate reduction in separated chiken hepatocytes. The cellular ascorbate concentration was elevated in dehydroascorbate-treated cells. It is thought that hepatocytes incorporated external dehydroascorbate and converted it into ascorbate. These findings suggest that the liver plays an important role in ascorbate recycling by the chicken.     

Atpif1基因对K562细胞血红蛋白合成的影响*

目的:探讨线粒体三磷酸腺苷酶抑制因子-1(Atpif1)对血红蛋白合成的影响。方法:首先,将K562细胞分为低氧实验组、常氧对照组,低氧实验组采用O₂浓度为2%,分别培养24 h,48 h,72 h后收集两组细胞,通过细胞增殖-毒性检测试剂盒(CCK8)法检测细胞的活性,流式细胞仪检测低氧对细胞凋亡的影响,通过氯化血红素诱导K562细胞,检测低氧对血红蛋白合成的影响,qRT-PCR检测Atpif1,核因子(NF-κB),delta-氨基酮戊酸合成酶2(Alas2)基因的转录表达。然后,将K562细胞置于低氧培养箱培养并分为空白组,阴性对照组和si-Atpif1三组。转染siRNA,沉默Atpif1基因,观察血红蛋白合成和NF-κB、Alas2基因mRNA水平变化。结果:与常氧对照组相比,低氧实验组K562细胞活性降低、凋亡增加,血红蛋白含量增加(P＜0.05)。Atpif1、Alas2、NF-κB的mRNA表达水平上调(P＜0.05)。与空白对照组和阴性对照组相比,si-Atpif1组血红蛋白含量均有减少(P＜0.05),同时NF-κB、Alas2的mRNA水平也出现下调(P＜0.05)。结论:Atpif1基因参与调控血红蛋白合成,探究其在高原红细胞增多症(HAPC)发生中的作用,可以为防治HAPC提供新的思路和治疗靶点。     

Induction of G2/M phase arrest by squamocin in chronic myeloid leukemia (K562) cells

Squamocin is one of the annonaceous acetogenins and has been reported to have anticancer activity. Squamocin was found to inhibit the growth of K562 cells in a time- and dose-dependent manner. Cell cycle analysis showed G2/M phase arrest in K562 cells following 24 h exposure to squamocin. During the G2/M arrest, cyclin-dependent kinase inhibitors (CDKIs), p21 and p27 were increased in a dose-dependent manner. Analysis of the cell cycle regulatory proteins demonstrated that squamocin did not change the steady-state levels of Cdk2, Cdk4, cyclin A, cyclin B1, cyclin D3 and cyclin E, but decreased the protein levels of Cdk1 and Cdc25C. These results suggest that squamocin inhibits the proliferation of K562 cells via G2/M arrest in association with the induction of p21, p27 and the reduction of Cdk1 and Cdc25C kinase activities.     

磁场对环磷酰胺杀伤人白血病细胞K562协同作用的研究初报

目的:研究不同处理时间稳恒磁场协同抗癌药物环磷酰胺对人白血病细胞K5 6 2的杀伤作用。方法:K5 6 2细胞经不同浓度的环磷酰胺和/或磁场处理12h或2 4h后,MTT法检测。数据进行统计学分析处理。结果:单纯磁场处理时,磁场对K5 6 2细胞的杀伤作用表现在2 4h(P <0 .0 1) ;环磷酰胺单纯处理K5 6 2细胞12h ,在0 .4和0 .8mg/mL浓度时对肿瘤细胞的生长没有影响(P >0 .0 5 ) ,在1.6和3.2mg/mL浓度下环磷酰胺对细胞有杀伤作用(P <0 .0 1) ;0 .4mg/mL环磷酰胺联合磁场处理K5 6 2细胞12～2 4h后,细胞活性均极显著的低于单纯环磷酰胺处理组(P <0 .0 1)。结论:9mT稳恒磁场对环磷酰胺杀伤肿瘤细胞具有一定的协同作用,磁场处理可以增加环磷酰胺的抗肿瘤效应。     

反义寡核苷酸对K562细胞的抑制作用及诱导细胞凋亡的研究

目的研究bcr-abl硫代磷酸反义寡脱氧核糖核酸(Aspo)作用于K562细胞后,对细胞mRNA、蛋白水平的影响,以及诱导细胞凋亡情况。方法Aspo与K562细胞共培养后,用流式细胞仪检测P210蛋白表达及细胞凋亡率,RT-PCR半定量检测bcr-ablmRNA表达情况,电镜观察细胞凋亡的形态学改变。结果K562细胞经浓度大于5μmol/Lbcr-ablAspo处理24h,流式细胞仪检测细胞P210蛋白表达下调甚至完全受抑制,10μmol/Lbcr-ablAspo作用48h,细胞bcr-ablmRNA下降45%左右,当细胞初始浓度为1×104/ml时,Aspo作用120h细胞凋亡率20%～30%,当细胞数增加至1×105/ml时,Aspo作用48h即可使30%细胞发生凋亡,电镜下观察到典型凋亡细胞形态学改变。结论bcr-abl反义核酸对K562细胞mRNA水平具有抑制作用,同时还可诱导细胞凋亡。     

Sonodynamic therapy induces the interplay between apoptosis and autophagy in K562 cells through ROS

Sonodynamic therapy (SDT) is a relatively new approach in the treatment of various cancers including leukemia cells. The aim of this study is to investigate the occurrence of apoptosis and autophagy after treated by protoporphyrin IX (PpIX)-mediated SDT (PpIX-SDT) on human leukemia K562 cells as well as the relationship between them. Firstly, mitochondrial-dependent apoptosis was observed through morphological observation and biochemical analysis. Meanwhile, SDT was shown to induce autophagy in K562 cells, which caused an increase in EGFP-LC3 puncta cells, a conversion of LC3 II/I, formation of acidic vesicular organelles (AVOs) and co-localization between LC3 and LAMP2 (a lysosome marker). Besides, pretreatment with autophagy inhibitor 3-MA or bafilomycin A1 was shown to provide protection against autophagy and to enhance SDT-induced apoptosis and necrosis, while the apoptosis suppressor z-VAD-fmk failed to affect formation of autophagic vacuoles or partially prevented SDT-induced cytotoxicity, which suggested that SDT-induced autophagy functioned as a survival mechanism. Additionally, this study reported apparent apoptosis and autophagy with dependence on intracellular reactive oxygen species (ROS) production. Preliminary data showed that ROS scavenger N-acetylcysteine (NAC) effectively blocked the SDT induced accumulation of ROS, reversed sono-damage, cell apoptosis and autophagy. Taken together, these data indicate that autophagy may be cytoprotective in our experimental system, and the ROS caused by PpIX-SDT treatment may play an important role in initiating apoptosis and autophagy.     

Evaluation of some genes and proteins involved in apoptosis on human chronic myeloid leukemia cells (K562 cells) by datura innoxia leaves aqueous extract

Abstract

Datura innoxia (D. innoxia) has an extensive usage in traditional medicine and can also be used for intervention therapy in order to treat cancer. Despite of accomplishing some researches on D. innoxia mechanism, still our knowledge is very little about exact D. innoxia apoptotic mechanism on human chronic myeloid leukemia cells (K562 cells). This study purpose was to clarify the molecular mechanism of apoptosis, which was mediated by D. innoxia leaves aqueous extract in K562 cells. MTT assay and flow cytometry was applied in order to assess the viability and apoptosis induction of K562 cells and normal human lymphoid B cells in the D. innoxia presence. Finally, the expression of the apoptotic related genes (p53, BAX, BCL2, Caspases 3, 6, 7 and 9) were evaluated using quantitative Real-Time PCR. Western blot analysis was applied for assessing the protein expression. MTT results indicated that D. innoxia could inhibit the viability of K562 cells in a dose- and time-dependent manner. In parallel, D. innoxia inhibitory effect on normal human lymphoid B cells was lower in comparison with its effect on K562 cells at the same concentrations and same incubation time. Apoptosis induction in K562 cells after D. innoxia exposure was determined by flow cytometry. Apoptosis was activated by D. innoxia in K562 cells throughout increasing the expression of P53, BAX/BCL2 ratio, caspase 9, 3, 6, 7. Western blot analysis demonstrated significant increase in cleaved PARP-1 and cleaved caspase 3 in treated K562 cells with high D. innoxia leaves aqueous extract concentration. D. innoxia leaves trigger apoptosis in K562 cells throughout intrinsic apoptotic pathway.

Communicated by Ramaswamy H. Sarma     

FKBP-RAP-FRB系统转运BCR-ABL入核对K562细胞的增殖抑制效应

BCR-ABL融合蛋白是慢性粒细胞白血病（chronic myeloid leukemia,CML）发病的基础。其中,BCR-ABL只能定位于细胞浆、不能易位至细胞核是其致病的关键因素。因此,转运BCR—ABL入核可能是治疗CML的潜在方法。该研究利用基因重组技术,构建HA-2FKBP-ABD（HF2A）和FLAG-3NLS—FRB＊（FN3R）重组腺病毒,与雷帕霉素类似物（Rapamycin analog）同组成FKBP-RAP-FRB系统,转运K562细胞胞浆中的BCR—ABL癌蛋白至细胞核,并探究其对K562细胞增殖的影响。结果显示,成功构建了高滴度的重组腺病毒,Westernblot证实目的蛋白在K562细胞内成功表达。FKBP—RAP—FRB系统可通过转运BCR—ABLA入核。抑制K562细胞生长和克隆形成的能力。结果揭示,FKBP-RAP—FRB系统转运BCR—ABL入核有望为CML提供新的治疗手段。