Role of intracellular Ca2+ signal in the ascorbate-induced apoptosis in a human hepatoma cell line

Exogenous iron impairs the anti-cancer effect of ascorbic acid both in vitro and in vivo

INTRODUCTION

The anti-cancer effect of high concentrations of ascorbic acid (AA) has been well established while its underlying mechanisms remain unclear. The association between iron and AA has attracted great attention but was still controversial due to the complicated roles of iron in tumors.

OBJECTIVES

Our study aims to explore the anti-cancer mechanisms of AA and the interaction between AA and iron in cancer.

METHODS

The MTT and ATP assays were used to evaluate the cytotoxicity of AA. Reactive oxygen species (ROS) generation, calcium (Ca²⁺), and lipid peroxidation were monitored with flow cytometry. Mitochondrial dysfunction was assessed by mitochondrial membrane potential (MMP) detection with JC-1 or tetramethylrhodamine methyl ester (TMRM) staining. Mitochondrial swelling was monitored with MitoTracker Green probe. FeSO₄ (Fe²⁺), FeCl₃ (Fe³⁺), Ferric ammonium citrate (Fe³⁺), hemin chloride (Fe³⁺) were used as an iron donor to investigate the effects of iron on AA's anti-tumor activity. The in vivo effects of AA and iron were analyzed in xenograft zebrafish and allograft mouse models.

RESULTS

High concentrations of AA exhibited cytotoxicity in a panel of cancer cells. AA triggered ROS-dependent non-apoptotic cell death. AA-induced cell death was essentially mediated by the accumulated intracellular Ca²⁺, which was partly originated from endoplasmic reticulum (ER). Surprisingly, exogenous iron could significantly reverse AA-induced ROS generation, Ca²⁺ overloaded, and cell death. Especially, the iron supplements significantly impaired the in vivo anti-tumor activity of AA.

CONCLUSIONS

Our study elucidated the protective roles of iron in ROS/Ca²⁺ mediated necrosis triggered by AA both in vitro and in vivo, which might shed novel insight into the anti-cancer mechanisms and provide clinical application strategies for AA in cancer treatment.

The Configuration-Dependent Anti-Leukemic Effect of Manoalide Stereoisomers: Reignite Research Interest in these Sponge-Derived Sesterterpenoids

Manoalide was studied as a potential anti-inflammatory agent for the last forty years and more than 200 publications and 180 patents were reported on this compound. However, the configurations at positions 24 and 25 and configuration-dependent bioactivity were not yet studied. In the current report, ten manoalide-like sesterterpenoids were isolated from Luffariella sp. (1-10). These stereoisomers were identified and separated for the first time since 1980 and their configurations at positions 24 and 25 were determined by analyzing their spectroscopic spectra. The configuration-dependent anti-proliferative activity of manoalide derivatives was examined by evaluating their effect on four leukemic cancer cell lines (Molt 4, K562, Sup-T1, and U937). The 24R,25S-isomers exhibited the most potent activity (IC₅₀ 0.50-7.67 μM). The anti-proliferative mechanism of action of 24R,25S-manoalide (7) was further studied on Molt 4 cells. Compound 7 exhibited apoptotic activity on Molt 4 cells through the disruption of mitochondrial membrane potential (MMP) and the generation of intracellular reactive oxygen species (ROS). It also inhibited the activity of human topoisomerase I and II. The apoptotic-inducing effect of 7 was further supported by the in vivo experiment by suppressing the volume of xenograft tumor growth (66.11%) compared with the control.

Selective cytotoxic activity and protective effects of sodium ascorbate against hepatocellular carcinoma through its effect on oxidative stress and apoptosis in vivo and in vitro

Objectives: Hepatocellular carcinoma (HCC) is characterized by elevated in oxidative stress and inflammatory cytokines, which enhance destructive effects of the tumor. Therefore, we conducted this study to investigate the protective effects of sodium ascorbate against thioacetamide-induced HCC in rats through studying its effect on the apoptotic pathway in rats. In addition, in vitro activity of sodium ascorbate was investigated on HepG2 and compared with cisplatin.

Methods: HCC was experimentally induced by injecting rats with 200 mg/kg thioacetamide intraperitoneally twice weekly for 16 weeks. Part of HCC rats was concomitantly treated with 100 mg/kg sodium ascorbate intraperitoneally during the 16-week period. Hepatic tissues were used for the determination of NFκB, Nrf2, TNF-α, caspase-3, caspase-8 and caspase-9.

Results: Sodium ascorbate significantly attenuated HCC-induced reduction in the expression of NrF2 associated with a reduction in concentrations of hydrogen peroxide and superoxide anion. In addition, sodium ascorbate blocked HCC-induced increase in the expression of NFκB and TNF-α. Sodium ascorbate slightly increased the activity of caspase-3, -8 and -9 in vitro but inhibited their activities in vivo.

Conclusion: In spite of the antioxidant and anti-inflammatory activity of sodium ascorbate, it produced selective cytotoxic activity via direct activation of the apoptotic pathway in cancer cells without affecting the apoptotic pathway in normal hepatic cells.

Cytotoxic and partial hepatoprotective activity of sodium ascorbate against hepatocellular carcinoma through inhibition of sulfatase-2 in vivo and in vitro

Hepatocellular carcinoma (HCC) is characterized by elevation in the activity of sulfatase-2, an extracellular enzyme that catalyzes removal of 6-O-sulfate groups from heparan sulfate. Therefore, we conducted this study to investigate the cytotoxic activity of the strong water-soluble antioxidant, sodium ascorbate, against HCC both in vivo and in vitro. Sodium ascorbate enhanced animal survival in vivo and reduced HepG2 cells survival. The protein levels of heparan sulfate proteoglycans (HSPGs), insulin like growth factor (IGF)-2, sulfatase-2 and glypican-3 were assessed. Inflammation was evaluated by measuring the gene and protein expression of NFκB, TNF-α, IL-1β, IL-4, IL-6 and IL-10. We found that sodium ascorbate blocked HCC-induced activation of sulfatase-2 leading to restoration of HSPGs receptors associated with reduction in IGF-2 and glypican-3. Sodium ascorbate exerts anti-inflammatory activity by reducing the expression of NFκB, CRP, TNF-α, IL-1β and IL-6 associated with enhanced expression of the anti-inflammatory cytokines, IL-4 and IL-10. In conclusion, cytotoxic effects of sodium ascorbate against HCC can be partially explained by inhibition of sulfatase-2, restoration of HSPGs receptors and deactivation of the inflammatory pathway.

Enhanced antitumor activity of vitamin C via p53 in cancer cells

Ascorbate is an important natural antioxidant that can selectively kill cancer cells at pharmacological concentrations. Despite its benefit, it is quite difficult to predict the antitumor effects of ascorbate, because the relative cytotoxicity of ascorbate differs between cancer cell lines. Therefore, it is essential to examine the basis for this fundamental disagreement. Because p53 is activated by DNA-damaging stress and then regulates various cellular conditions, we hypothesized that p53 can sensitize cancer cells to ascorbate. Using isogenic cancer cells, we observed that the presence of p53 can affect ascorbate cytotoxicity, and also reactivation of p53 can make cancer cells sensitive to ascorbate. p53-dependent enhancement of ascorbate cytotoxicity is caused by increased reactive oxygen species generation via a differentially regulated p53 transcriptional network. We also found that transcriptionally activated p53 was derived from MDM2 ubiquitination by ascorbate and subsequently its signaling network renders cancer cells more susceptible to oxidative stress. Similar to the p53 effect on in vitro ascorbate cytotoxicity, inhibition of tumor growth is also stronger in p53-expressing tumors than in p53-deficient ones in vivo. This is the first observation that ascorbate cytotoxicity is positively related to p53 expression, activating its transcriptional network to worsen intracellular oxidative stress and consequently enhancing its cytotoxicity. Based on our study, reactivation of p53 may help to achieve more consistent cytotoxic effects of ascorbate in cancer therapies.

A novel targeting modality for renal cell carcinoma: human osteocalcin promoter-mediated gene therapy synergistically induced by vitamin C and vitamin D₃

BACKGROUND

Advanced renal cell carcinoma (RCC) frequently develops skeletal metastasis and is highly resistant to conventional therapies. We hypothesized that the osteocalcin (OC) promoter may be a promising gene delivery system for RCC targeted gene therapy because osteotropic tumors gain osteomimetic properties and thrive in the new environment by exhibiting a bone-like gene expression profile. Human OC (hOC) expression is highly regulated by vitamins and hormone. In the present study, we tested the feasibility of vitamin-regulatable hOC promoter for RCC-specific transcriptional targeting, and examined the anti-tumor effect of vitamins C and D₃ with hOC-based adenoviral vectors towards RCC.

METHODS

Real-time reverse transcriptase-polymerase chain reaction measured OC expression induced by vitamins C and D₃, either alone or in combination, in RCC and normal human renal epithelial cells (HRE). The RCC-cytotoxic effects of concomitant vitamins and hOC promoter-based adenoviral vectors, Ad-hOC-TK and Ad-hOC-E1, were evaluated in both cell culture and a xenograft murine model.

RESULTS

We found that high doses of vitamin C induced H₂O₂-dependent apoptosis in RCC but not HRE. Treatment of RCC cells with combined vitamins C and D₃ treatment significantly increased OC promoter activity compared to single reagent treatment. Combined vitamin therapy reduced tumor size (85%) and complete tumor regression occurred in 38% of mice co-administrated Ad-hOC-E1.

CONCLUSIONS

The results obtained in the present study demonstrate that vitamins C and D₃ synergized with the anti-tumor effects of therapeutic genes driven by hOC promoter through direct cytotoxicity as well as transcriptional targeting. This combined gene therapy provides a promising modality for advanced RCC targeted therapy.

Crocetin prevents AGEs-induced vascular endothelial cell apoptosis

Advanced glycation end products (AGEs) are causally correlated with diabetic vascular complications. AGEs triggered oxidative reaction then accelerated endothelial cell apoptosis is a critical event in the process of vascular complications. Crocetin, a carotenoid has been previously shown to have strong antioxidant activates. Therefore, this study was designed to investigate the role of crocetin on the prevention of AGEs-mediated cell apoptosis in bovine aortic endothelial cells (BEC) and the mechanisms involved. Exposure of BEC to 200 microg/ml AGEs for 48 h results in a significant increase in apoptotic rate, compared with control. AGEs-induced DNA fragmentation preferentially occurred in the S phase cells. Crocetin prevented AGEs-induced BEC apoptosis, which correlates with crocetin attenuation of AGEs mediated increase of intracellular reactive oxygen species (ROS) formation and elevation of intracellular Ca2+ concentration ([Ca2+]i) level (P<0.01 versus AGEs group). These results demonstrate that crocetin prevents AGEs-induced BEC apoptosis through ROS inhibition and [Ca2+]i stabilization and suggest that crocetin may exert a beneficial effect in preventing diabetes-associated vascular complications.

Mechanisms of enhanced taurine release under Ca2+ depletion

The sulfur-containing amino acid taurine is an inhibitory neuromodulator in the brain of mammals, as well as a key substance in the regulation of cell volumes. The effect of Ca(2+) on extracellular taurine concentrations is of special interest in the context of the regulatory mechanisms of taurine release. The aim of this study was to characterize the basal release of taurine in Ca(2+)-free medium using in vivo microdialysis of the striatum of anesthetized rats. Perfusion of Ca(2+)-free medium via a microdialysis probe evoked a sustained release of taurine (up to 180 % compared to the basal levels). The Ca(2+) chelator EGTA (1mM) potentiated Ca(2+) depletion-evoked taurine release. The substitution of CaCl(2) by choline chloride did not alter the observed effect. Ca(2+)-free solution did not significantly evoke release of taurine from tissue loaded with the competitive inhibitor of taurine transporter guanidinoethanesulfonate (1mM), suggesting that in Ca(2+) depletion taurine is released by the transporter operating in the outward direction. The volume-sensitive chloride channel blocker diisothiocyanostilbene-2,2'-disulfonate (1mM) did not attenuate the taurine release evoked by Ca(2+) depletion. The non-specific blocker of voltage-sensitive Ca(2+) channels NiCl(2) (0.65 mM) enhanced taurine release in the presence of Ca(2+). CdCl(2) (0.25 mM) had no effect under these conditions. However, both CdCl(2) and NiCl(2) attenuated the effect of Ca(2+)-free medium on the release of taurine. The data obtained imply the involvement of both decreased influx of Ca(2+) and increased non-specific influx of Na(+) through voltage-sensitive calcium channels in the regulation of transporter-mediated taurine release in Ca(2+) depletion.