Cellular Uptake of Epigallocatechin Gallate in Comparison to Its Major Oxidation Products and Their Antioxidant Capacity In Vitro

Depletion of reactive oxygen species and reduction of oxidative stress have been identified as key parameters in the prevention of cellular aging. In previous in vitro studies, the tea catechin epigallocatechin gallate (EGCG) was found to have both pro- and antioxidant properties, disregarding the low stability under cell culture conditions. Besides hydrogen peroxide, theasinensin dimers amongst other oxidation products are formed. Exact quantities, cellular uptake and antioxidant capacities of these dimeric oxidation products remain unknown. Via high-performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS/MS), formation kinetics and cellular uptake of EGCG and its major oxidation products are quantified. The antioxidant capacity is determined on a cellular level using a modified dichlorofluorescein (DCF) approach. As a first result, oxidation product quantities of up to 21 µM each are measured after incubation of 50 µM EGCG. While EGCG is taken up equimolarly, its major oxidation products are accumulated in hepatocarcinoma HepG2 cells at millimolar concentrations, especially theasinensin A (TSA). Lastly, the oxidation products show higher antioxidant properties than the monomer EGCG. In correlation with cellular uptake, TSA displays the highest capacity of all tested analytes. The findings reveal the strong influence of EGCG oxidation products on its bioactivity in vitro.

Intracellular ROS profile in hematopoietic progenitors of MDS patients: association with blast count and iron overload

Objectives: Reactive oxygen species (ROS) are under scrutiny as a participant in the pathophysiology of myelodysplastic syndrome (MDS) and the progression of MDS to acute myeloid leukemia (AML). Measurement of intracellular ROS (iROS) is particularly important since iROS is a direct indicator of cellular health and integrity.Methods: We developed a technique to measure standardize iROS (siROS) level in lymphocytes and bone marrow (BM) CD34⁺ hematopoietic progenitors using the fluorescent probe dichlorofluorescein (DCF). We then quantified the siROS in 38 consecutive BM specimens from 27 MDS patients over the course of 10 months. Disease outcome of these patients were also assessed.Results: High serum ferritin, high blast count and poor IPSS were associated with inferior survival and AML progression in this cohort. High blast MDS patients had lower siROS in their BM CD34+ cells than those of low blast patients, consistent with increased reliance on glycolysis and enhanced ROS defense in high blast MDS. We also observed narrower siROS distribution in the BM CD34+ cells of high blast patients, suggesting that loss of heterogeneity in ROS content accompanies the clonal evolution of MDS. Furthermore, we observed a strong correlation between CD34+ cells siROS and serum ferritin level in high blast patients. In one case, iron chelation therapy (ICT) resulted in parallel decreases in serum ferritin and CD34⁺ cells siROS.Conclusion: Our findings established the siROS profile in early hematopoietic cells of MDS patients and its relationship with blast count and iron overload.

Mitochondrial translocator protein (TSPO) ligands prevent doxorubicin-induced mechanical dysfunction and cell death in isolated cardiomyocytes

Contractile dysfunction and subsequent development of cardiomyopathies are well known limiting factors in the treatment of cancer with doxorubicin and have been linked to mitochondrial dysfunction. Here, using adult isolated paced cardiomyocytes, we have demonstrated that ligands of translocator protein (TSPO) 4'-chlorodiazepam and TRO40303 prevented the doxorubicin-induced alterations in contractility and improved cardiomyocyte viability. This cardioprotective effect was closely associated with both a potent reduction in reactive oxygen species production and inhibition of mitochondrial permeability transition pore opening. Thus, preventive administration of TSPO ligands may represent a novel pharmacological strategy to protect the heart during doxorubicin treatment.

Cytotoxicity and modes of action of four Cameroonian dietary spices ethno-medically used to treat cancers: Echinops giganteus, Xylopia aethiopica, Imperata cylindrica and Piper capense

ETHNOPHARMACOLOGICAL RELEVANCE

Echinops giganteus, Imperata cylindrica, Piper capense and Xylopia aethiopica are four medicinal spices used in Cameroon to treat cancers.

AIM OF THE STUDY

The above plants previously displayed cytotoxicity against leukemia CCRF-CEM and CEM/ADR5000 cell lines as well as human pancreatic MiaPaCa-2 cells. The present study aims at emphasizing the study of the cytotoxicity and the modes of action of the above plants on a panel of ten cancer cell lines including various sensitive and drug-resistant phenotypes. The study has been extended to the isolation of the bioactive constituents from Echinops giganteus.

MATERIALS AND METHODS

The cytotoxicity of the extracts was determined using a resazurin reduction assay, whereas the caspase-Glo assay was used to detect the activation of caspases 3/7, caspase 8 and caspase 9 in cells treated with the four extracts. Flow cytometry was used for cell cycle analysis and detection of apoptotic cells, analysis of mitochondrial membrane potential (MMP) as well as measurement of reactive oxygen species (ROS).

RESULTS

The four tested extracts inhibited the proliferation of all tested cancer cell lines including sensitive and drug-resistant phenotypes. Collateral sensitivity of cancer cells to the extract of Echinops giganteus was generally better than to doxorubicin. The recorded IC50 ranges were 3.29 µg/mL [against human knockout clones HCT116 (p53(-/-)) colon cancer cells] to 14.32 µg/mL (against human liver hepatocellular carcinoma HepG2 cells) for the crude extract from Echinops giganteus, 4.17 µg/mL (against breast cancer cells transduced with control vector MDA-MB231 cells) to 19.45 µg/mL (against MDA-MB-231 BCRP cells) for that of Piper capense, 4.11 µg/mL (against leukemia CCRF-CEM cells) to 30.60 µg/mL (against leukemia HL60AR cells) for Xylopia aethiopica, 3.28 µg/mL [against HCT116 (p53(-/-)) cells] to 33.43 µg/mL (against HepG2 cells) for Imperata cylindica and 0.11 µg/mL (against CCRF-CEM cells) to 132.47 µg/mL (against HL60AR cells) for doxorubicin. The four tested extracts induced apoptosis in CCRF-CEM cells via the alteration loss of MMP whilst that of Piper capense also enhanced the production of ROS.

CONCLUSION

The studied plants are potential cytotoxic drugs that deserve more detailed exploration in the future, to develop novel anticancer drugs against sensitive and otherwise drug-resistant phenotypes.

Negative modulation of mitochondrial oxidative phosphorylation by epigallocatechin-3 gallate leads to growth arrest and apoptosis in human malignant pleural mesothelioma cells

Increasing evidence reveals a large dependency of epithelial cancer cells on oxidative phosphorylation (OXPHOS) for energy production. In this study we tested the potential of epigallocatechin-3-gallate (EGCG), a natural polyphenol known to target mitochondria, in inducing OXPHOS impairment and cell energy deficit in human epitheliod (REN cells) and biphasic (MSTO-211H cells) malignant pleural mesothelioma (MMe), a rare but highly aggressive tumor with high unmet need for treatment. Due to EGCG instability that causes H2O2 formation in culture medium, the drug was added to MMe cells in the presence of exogenous superoxide dismutase and catalase, already proved to stabilize the EGCG molecule and prevent EGCG-dependent reactive oxygen species formation. We show that under these experimental conditions, EGCG causes the selective arrest of MMe cell growth with respect to normal mesothelial cells and the induction of mitochondria-mediated apoptosis, as revealed by early mitochondrial ultrastructure modification, swelling and cytochrome c release. We disclose a novel mechanism by which EGCG induces apoptosis through the impairment of mitochondrial respiratory chain complexes, particularly of complex I, II and ATP synthase. This induces a strong reduction in ATP production by OXPHOS, that is not adequately counterbalanced by glycolytic shift, resulting in cell energy deficit, cell cycle arrest and apoptosis. The EGCG-dependent negative modulation of mitochondrial energy metabolism, selective for cancer cells, gives an important input for the development of novel pharmacological strategies for MMe.

Formononetin potentiates epirubicin-induced apoptosis via ROS production in HeLa cells in vitro

The frequent development of multidrug resistance (MDR) hampers the efficacy of available anticancer drugs in treating cervical cancer. In this study, we aimed to use formononetin (7-hydroxy-4'-methoxyisoflavone), a potential herbal isoflavone, to intensify the chemosensitivity of human cervical cancer HeLa cells to epirubicin, an anticancer drug. The reactive oxygen species (ROS) levels were correlated with MDR modulation mechanisms, including the transporter inhibition and apoptosis induction. Our results revealed that formononetin significantly enhanced the cytotoxicity of epirubicin. Co-incubation of epirubicin with formononetin increased the ROS levels, including hydrogen peroxide and superoxide free radicals. Epirubicin alone markedly increased the mRNA expression of MDR1, MDR-associated protein (MRP) 1, and MRP2. In contrast, formononetin alone or combined treatment decreased the mRNA expression of MRP1 and MRP2. This result indicates that efflux transporter-mediated epirubicin resistance is inhibited at different degrees by the addition of formononetin. This isoflavone significantly intensified epirubicin uptake into HeLa cells. Apoptosis was induced by formononetin and/or epirubicin, as signified by nuclear DNA fragmentation, chromatin condensation, increased sub-G1 and G2/M phases. The cotreatment triggered the mitochondrial apoptotic pathway indicated by increased Bax-to-Bcl-2 expression ratio, loss of mitochondrial membrane potential, and significant activation of caspase-9 and -3. In addition, extrinsic/caspases-8 apoptotic pathway was also induced by the cotreatment. N-acetyl cysteine abrogated these events induced by formononetin, supporting the involvement of ROS in the MDR reversal mechanism. This study pioneered in demonstrating that formononetin may potentiate the cytotoxicity of epirubicin in HeLa cells through the ROS-mediated MRP inhibition and concurrent activation of the mitochondrial and death receptor pathways of apoptosis. Hence, the circumvention of pump and non-pump resistance using formononetin and epirubicin may pave the way for a powerful chemotherapeutic regimen for treating human cervical cancer.

Antioxidant effects of diallyl trisulfide on high glucose-induced apoptosis are mediated by the PI3K/Akt-dependent activation of Nrf2 in cardiomyocytes

BACKGROUND

Hyperglycemia-induced reactive oxygen species (ROS) generation contributes to development of diabetic cardiomyopathy. Nuclear factor E2-related factor 2 (Nrf2), a redox-sensing transcription factor, induces the antioxidant enzyme expressions. Diallyl trisulfide (DATS) is the most powerful antioxidant among the sulfur-containing compounds in garlic oil. We investigated whether DATS inhibits hyperglycemia-induced ROS production via Nrf2-mediated activation of antioxidant enzymes in cardiac cells exposed to high glucose (HG).

METHODS AND RESULTS

Treatment of H9c2 cells with HG resulted in an increase in intracellular ROS level and caspase-3 activity, which were markedly reduced by the administration of DATS (10 μM). DATS treatment significantly increased Nrf2 protein stability and nuclear translocation, upregulated downstream gene HO-1, and suppressed its repressor Keap1. However, apoptosis was not inhibited by DATS in cells transfected with Nrf2-specific siRNA. Inhibition of PI3K/Akt signaling by LY294002 (PI3K inhibitor) or PI3K-specific siRNA not only decreased the level of DATS-induced Nrf2-mediated HO-1 expression, but also diminished the protective effects of DATS. Similar results were also observed in high glucose-exposed neonatal primary cardiomyocytes and streptozotocin-treated diabetic rats fed DATS at a dose of 40 mg/kg BW.

CONCLUSIONS

Our findings indicate that DATS protects against hyperglycemia-induced ROS-mediated apoptosis by upregulating the PI3K/Akt/Nrf2 pathway, which further activates Nrf2-regulated antioxidant enzymes in cardiomyocytes exposed to HG.