ROS-driven and preferential killing of HepG2 over L-02 cells by a short-term cooperation of Cu(II) and a catechol-type resveratrol analog

From polyphenol to o-quinone: Occurrence, significance, and intervention strategies in foods and health implications

Polyphenol oxidation is a chemical process impairing food freshness and other desirable qualities, which has become a serious problem in fruit and vegetable processing industry. It is crucial to understand the mechanisms involved in these detrimental alterations. o-Quinones are primarily generated by polyphenols with di/tri-phenolic groups through enzymatic oxidation and/or auto-oxidation. They are highly reactive species, which not only readily suffer the attack by nucleophiles but also powerfully oxidize other molecules presenting lower redox potentials via electron transfer reactions. These reactions and subsequent complicated reactions are capable of initiating quality losses in foods, such as browning, aroma loss, and nutritional decline. To attenuate these adverse influences, a variety of technologies have emerged to restrain polyphenol oxidation via governing different factors, especially polyphenol oxidases and oxygen. Despite tremendous efforts devoted, to date, the loss of food quality caused by quinones has remained a great challenge in the food processing industry. Furthermore, o-quinones are responsible for the chemopreventive effects and/or toxicity of the parent catechols on human health, the mechanisms by which are quite complex. Herein, this review focuses on the generation and reactivity of o-quinones, attempting to clarify mechanisms involved in the quality deterioration of foods and health implications for humans. Potential innovative inhibitors and technologies are also presented to intervene in o-quinone formation and subsequent reactions. In future, the feasibility of these inhibitory strategies should be evaluated, and further exploration on biological targets of o-quinones is of great necessity.

How to Use Respiratory Chain Inhibitors in Toxicology Studies-Whole-Cell Measurements

Mitochondrial electron transport chain (ETC) inhibition is a phenomenon interesting in itself and serves as a tool for studying various cellular processes. Despite the fact that searching the term “rotenone” in PubMed returns more than 6900 results, there are many discrepancies regarding the directions of changes reported to be caused by this RTC inhibitor in the delicate redox balance of the cell. Here, we performed a multifaceted study of the popular ETC inhibitors rotenone and antimycin A, involving assessment of mitochondrial membrane potential and the production of hydrogen peroxide and superoxide anions at cellular and mitochondrial levels over a wide range of inhibitor concentrations (1 nmol/dm³–100 µmol/dm³). All measurements were performed with whole cells, with accompanying control of ATP levels. Antimycin A was more potent in hindering HepG2 cells’ abilities to produce ATP, decreasing ATP levels even at a 1 nmol/dm³ concentration, while in the case of rotenone, a 10,000-times greater concentration was needed to produce a statistically significant decrease. The amount of hydrogen peroxide produced in the course of antimycin A biological activity increased rapidly at low concentrations and decreased below control level at a high concentration of 100 µmol/dm³. While both inhibitors influenced cellular superoxide anion production in a comparable manner, rotenone caused a greater increase in mitochondrial superoxide anions compared to a modest impact for antimycin A. IC50 values for rotenone and antimycin A with respect to HepG2 cell survival were of the same order of magnitude, but the survival curve of cells treated with rotenone was clearly biphasic, suggesting a concentration-dependent mode of biological action. We propose a clear experimental setup allowing for complete and credible analysis of the redox state of cells under stress conditions which allows for better understanding of the effects of ETC inhibition.

Prooxidative inhibition against NF-κB-mediated inflammation by pharmacological vitamin C

Vitamin C (VC), widely found in vegetables and fruits, operates as an electron donor to perform various biological functions including anti-inflammatory activity. However, the mechanisms by which VC inhibits inflammation remain insufficiently understood. Accordingly, we performed a detail mechanistic study on anti-inflammatory activity of VC at millimolar (pharmacological) concentrations in lipopolysaccharides-stimulated RAW264.7 cells. It was found that VC and its two-electron oxidative product, dehydroascorbate (DHA) constructs an efficient redox cycle with the aid of intracellular glutathione and copper ions, thereby facilitating the generation of reactive oxygen species (ROS) and the ROS-dependent inhibition against the NF-κB-mediated inflammation.

Targeting the redox imbalance in mitochondria: A novel mode for cancer therapy

Changes in reactive oxygen species (ROS) levels affect many aspects of cell behavior. During carcinogenesis, moderate ROS production modifies gene expression to alter cell function, elevating metabolic activity and ROS. To avoid extreme ROS-activated death, cancer cells increase antioxidative capacity, regulating sustained ROS levels that promote growth. Anticancer therapies are exploring inducing supranormal, cytotoxic oxidative stress levels either inhibiting antioxidative capacity or promoting excess ROS to selectively destroy cancer cells, triggering mechanisms such as apoptosis, autophagy, necrosis, or ferroptosis. This review exemplifies pro-oxidants (natural/synthetic/repurposed drugs) and their clinical significance as cancer therapies providing revolutionary approaches.

Antiproliferative Effect and Mediation of Apoptosis in Human Hepatoma HepG2 Cells Induced by Djulis Husk and Its Bioactive Compounds

The antiproliferative effect and mediation of apoptosis in human hepatoma HepG2 cells induced by djulis husk and its bioactive compounds was investigated. The ethanolic extracts of djulis husk (EEDH) at 50, 250, and 500 µg/mL induced remarkable cytotoxicity on HepG2 cells. By flow cytometry analysis, EEDH slowed down the cell cycle at the Sub-G0 phase after 24 h of incubation. Moreover, all EEDH treatment induced an apoptotic response in HepG2 cells. EEDH-induced apoptosis was associated with the attenuation of mitochondrial transmembrane potentials (ΔΨ_m), an increase in Bax/Bcl-2 ratio, activation of caspase-3, and poly(ADP-ribose)polymerase (PARP) cleavage, as well as an increase in reactive oxygen species (ROS) generation. According to the HPLC-DAD and HPLC-MS/MS analysis, quercetin and kaempferol derivatives and another sixteen compounds were present in EEDH. Quercetin and kaempferol at 25–150 μM showed antiproliferative action and induced apoptosis on HepG2 cells, which may in part account for the anticancer activity of EEDH. Overall, EEDH may be a potent chemopreventive agent due to apoptosis in HepG2 cells.

Small molecules regulating reactive oxygen species homeostasis for cancer therapy

Elevated intracellular reactive oxygen species (ROS) and antioxidant defense systems have been recognized as one of the hallmarks of cancer cells. Compared with normal cells, cancer cells exhibit increased ROS to maintain their malignant phenotypes and are more dependent on the "redox adaptation" mechanism. Thus, there are two apparently contradictory but virtually complementary therapeutic strategies for the regulation of ROS to prevent or treat cancer. The first strategy, that is, chemoprevention, is to prevent or reduce intracellular ROS either by suppressing ROS production pathways or by employing antioxidants to enhance ROS clearance, which protects normal cells from malignant transformation and inhibits the early stage of tumorigenesis. The second strategy is the ROS-mediated anticancer therapy, which stimulates intracellular ROS to a toxicity threshold to activate ROS-induced cell death pathways. Therefore, targeting the regulation of intracellular ROS-related pathways by small-molecule candidates is considered to be a promising treatment for tumors. We herein first briefly introduce the source and regulation of ROS, and then focus on small molecules that regulate ROS-related pathways and show efficacy in cancer therapy from the perspective of pharmacophores. Finally, we discuss several challenges in developing cancer therapeutic agents based on ROS regulation and propose the direction of future development.

Inhibiting NF-κB-Mediated Inflammation by Catechol-Type Diphenylbutadiene via an Intracellular Copper- and Iron-Dependent Pro-Oxidative Role

Chronic inflammation mediated by nuclear factor-κB (NF-κB) plays a crucial role in the development of cancer. As part of our continuous efforts placed on investigating anticancer mechanisms of dietary catechols, we further applied catechol-type diphenylbutadiene (3,4-DHB) as a model molecule to probe whether it inhibits inflammation by its pro-oxidative role. Employing lipopolysaccharide-stimulated RAW264.7 cells as a model of inflammation, we validated that benefiting from its catechol moiety, 3,4-DHB inhibited significantly the LPS-induced formation of NO (11.48 ± 0.39 μM) compared with the only LPS-stimulated group (31.8 ± 1.78 μM) with an inhibitory rate of 64% at 5 μM, expression of iNOS and COX-2 proteins, phosphorylation of IkB kinase and IkBα, and nuclear translocation of NF-κB. Noticeably, its inhibitory activity against the NF-κB-mediated inflammation can be obviously revised by pretreatment of the cells with dithiothreitol (a quencher of both electrophilic o-quinone and ROS), neocuproine (a specific chelating agent for copper ions), and deferoxamine (a specific chelating agent for iron ions). The above results support that depending on intracellular copper and iron ions, 3,4-DHB, a pro-electrophile, can be converted into its corresponding o-quinone electrophile together with the generation of ROS, a pro-oxidative event that mediates its inhibitory activity against NF-κB signaling and inflammation. The copper- and iron-dependent inhibition against inflammation supports that dietary catechols are probably pro-oxidative anti-inflammatory agents.

Resveratrol - A comprehensive review of recent advances in anticancer drug design and development

Resveratrol is a natural polyphenolic stilbene isolated from various plants, foods and beverages with a broad spectrum of biological and pharmacological properties through modulating diverse targets and signaling pathways. Particularly, it has attracted a great deal of attention as a promising and multitarget anticancer agent due to its potential use in chemoprevention and chemotherapy of various tumors. However, unfavorable pharmacokinetics/pharmacodynamics profile such as poor bioavailability restricted its applications. Therefore, medicinal chemists have synthesized a lot of novel derivatives and analogues of resveratrol using different modification strategies to overcome these limitations and improve anticancer efficacy. Herein, we reviewed the design, synthesis, structure-activity relationship and mechanism of the most potent and privileged resveratrol-based compounds that showed promising anticancer activities in the last five years. We classified these compounds into the ten different categories based on their chemical structure similarities.

Natural products and phytochemical nanoformulations targeting mitochondria in oncotherapy: an updated review on resveratrol

Mitochondria are intracellular organelles with two distinct membranes, known as an outer mitochondrial membrane and inner cell membrane. Originally, mitochondria have been derived from bacteria. The main function of mitochondria is the production of ATP. However, this important organelle indirectly protects cells by consuming oxygen in the route of energy generation. It has been found that mitochondria are actively involved in the induction of the intrinsic pathways of apoptosis. So, there have been efforts to sustain mitochondrial homeostasis and inhibit its dysfunction. Notably, due to the potential role of mitochondria in the stimulation of apoptosis, this organelle is a promising target in cancer therapy. Resveratrol is a non-flavonoid polyphenol that exhibits significant pharmacological effects such as antioxidant, anti-diabetic, anti-inflammatory and anti-tumor. The anti-tumor activity of resveratrol may be a consequence of its effect on mitochondria. Multiple studies have investigated the relationship between resveratrol and mitochondria, and it has been demonstrated that resveratrol is able to significantly enhance the concentration of reactive oxygen species, leading to the mitochondrial dysfunction and consequently, apoptosis induction. A number of signaling pathways such as sirtuin and NF-κB may contribute to the mitochondrial-mediated apoptosis by resveratrol. Besides, resveratrol shifts cellular metabolism from glycolysis into mitochondrial respiration to induce cellular death in cancer cells. In the present review, we discuss the possible interactions between resveratrol and mitochondria, and its potential application in cancer therapy.

Identification of Catechol-Type Diphenylbutadiene as a Tyrosinase-Activated Pro-oxidative Chemosensitizer against Melanoma A375 Cells via Glutathione S-Transferase Inhibition

Glutathione S-transferases (GSTs) play an active role in the development of drug resistance by numerous cancer cells, including melanoma cells, which is a major cause of chemotherapy failure. As part of our continuous effort to explore why dietary polyphenols bearing the catechol moiety (dietary catechols) show usually anticancer activity, catechol-type diphenylbutadiene (3,4-DHB) was selected as a model of dietary catechols to probe whether they work as pro-oxidative chemosensitizers via GST inhibition in melanoma cells. It was found that, in human melanoma A375 cells, 3,4-DHB is easily converted to its ortho-quinone via copper-containing tyrosinase-mediated two-electron oxidation along with generation of reactive oxygen species (ROS) derived from the oxidation; the resulting ortho-quinone and ROS are responsible for its ability to sensitize the cisplatin-resistant cells by inhibiting GST, followed by induction of apoptosis in an ASK1-JNK/p38 signaling cascade and mitochondria-dependent pathway. This work provides further evidence to support that dietary catechols exhibit antimelanoma activity by virtue of their tyrosinase-dependent pro-oxidative role and gives useful information for designing polyphenol-inspired GST inhibitors and sensitizers in chemotherapy against melanoma.

Tangeretin-Assisted Platinum Nanoparticles Enhance the Apoptotic Properties of Doxorubicin: Combination Therapy for Osteosarcoma Treatment

Osteosarcoma (OS) is the most common type of cancer and the most frequent malignant bone tumor in childhood and adolescence. Nanomedicine has become an indispensable field in biomedical and clinical research, with nanoparticles (NPs) promising to increase the therapeutic efficacy of anticancer drugs. Doxorubicin (DOX) is a commonly used chemotherapeutic drug against OS; however, it causes severe side effects that restrict its clinical applications. Here, we investigated whether combining platinum NPs (PtNPs) and DOX could increase their anticancer activity in human bone OS epithelial cells (U2OS). PtNPs with nontoxic, effective, thermally stable, and thermoplasmonic properties were synthesized and characterized using tangeretin. We examined the combined effects of PtNPs and DOX on cell viability, proliferation, and morphology, reactive oxygen species (ROS) generation, lipid peroxidation, nitric oxide, protein carbonyl content, antioxidants, mitochondrial membrane potential (MMP), adenosine tri phosphate (ATP) level, apoptotic and antiapoptotic gene expression, oxidative stress-induced DNA damage, and DNA repair genes. PtNPs and DOX significantly inhibited U2OS viability and proliferation in a dose-dependent manner, increasing lactate dehydrogenase leakage, ROS generation, and malondialdehyde, nitric oxide, and carbonylated protein levels. Mitochondrial dysfunction was confirmed by reduced MMP, decreased ATP levels, and upregulated apoptotic/downregulated antiapoptotic gene expression. Oxidative stress was a major cause of cytotoxicity and genotoxicity, confirmed by decreased levels of various antioxidants. Furthermore, PtNPs and DOX increased 8-oxo-dG and 8-oxo-G levels and induced DNA damage and repair gene expression. Combination of cisplatin and DOX potentially induce apoptosis comparable to PtNPs and DOX. To the best of our knowledge, this is the first report to describe the combined effects of PtNPs and DOX in OS.

Developing glutathione-activated catechol-type diphenylpolyenes as small molecule-based and mitochondria-targeted prooxidative anticancer theranostic prodrugs

Developing concise theranostic prodrugs is highly desirable for personalized and precision cancer therapy. Herein we used the glutathione (GSH)-mediated conversion of 2,4-dinitrobenzenesulfonates to phenols to protect a catechol moiety and developed stable pro-catechol-type diphenylpolyenes as small molecule-based prooxidative anticancer theranostic prodrugs. These molecules were synthesized via a modular route allowing creation of various pro-catechol-type diphenylpolyenes. As a typical representative, PDHH demonstrated three unique advantages: (1) capable of exploiting increased levels of GSH in cancer cells to in situ release a catechol moiety followed by its in situ oxidation to o-quinone, leading to preferential redox imbalance (including generation of H₂O₂ and depletion of GSH) and final selective killing of cancer cells over normal cells, and is also superior to 5-fluorouracil and doxorubicin, the widely used chemotherapy drugs, in terms of its ability to kill preferentially human colon cancer SW620 cells (IC₅₀ = 4.3 μM) over human normal liver L02 cells (IC₅₀ = 42.3 μM) with a favourable in vitro selectivity index of 9.8; (2) permitting a turn-on fluorescent monitoring for its release, targeting mitochondria and therapeutic efficacy without the need of introducing additional fluorophores after its activation by GSH in cancer cells; (3) efficiently targeting mitochondria without the need of introducing additional mitochondria-directed groups.

Effect of Cu/Mn-Fortification on In Vitro Activities of the Peptic Hydrolysate of Bovine Lactoferrin against Human Gastric Cancer BGC-823 Cells

Bovine lactoferrin hydrolysate (BLH) was prepared with pepsin, fortified with Cu2+ (Mn2+) 0.64 and 1.28 (0.28 and 0.56) mg/g protein, and then assessed for their activity against human gastric cancer BGC-823 cells. BLH and the four fortified BLH products dose- and time-dependently had growth inhibition on the cells in both short- and long-time experiments. These samples at dose level of 25 mg/mL could stop cell-cycle progression at the G0/G1-phase, damage mitochondrial membrane, and induce cell apoptosis. In total, the fortified BLH products had higher activities in the cells than BLH alone. Moreover, higher Cu/Mn fortification level brought higher effects, and Mn was more effective than Cu to increase these effects. In the treated cells, the apoptosis-related proteins such as Bad, Bax, p53, cytochrome c, caspase-3, and caspase-9 were up-regulated, while Bcl-2 was down-regulated. Caspase-3 activation was also evidenced using a caspase-3 inhibitor, z-VAD-fmk. Thus, Cu- and especially Mn-fortification of BLH brought health benefits such as increased anti-cancer activity in the BGC-823 cells via activating the apoptosis-related proteins to induce cell apoptosis.

Resveratrol Enhances Apoptotic and Oxidant Effects of Paclitaxel through TRPM2 Channel Activation in DBTRG Glioblastoma Cells

Numerous studies have reported a strong association between increased production of reactive oxygen species (ROS) and the pathobiology of several diseases, and cancer in particular. Therefore, manipulation of cellular oxidative stress levels represents an important therapeutic target. Recently, resveratrol (RESV), a naturally occurring phytochemical, has been shown to sensitize several cell lines to the anticancer effects of other chemotherapeutic agents, including paclitaxel (PAX). However, the molecular mechanisms of action of RESV through oxidative sensitive TRPM2 channel activation remain unclear. The aim of this study was to evaluate the effect of combination therapy of RESV and PAX on activation of TRPM2 in DBTRG glioblastoma cells. DBTRG cells were divided into four treatment groups: control, RESV (50 μM), PAX (50 μM), and PAX + RESV for 24 hours. Our data shows that markers for apoptosis, mitochondrial membrane depolarization and mitochondrial function, intracellular steady-state ROS levels, caspase 3 activity, TRPM2 current density, and Ca²⁺ florescence intensity were significantly increased in DBTRG cells following treatment with PAX and RESV, respectively, although cell viability was also decreased by these treatments. These biochemical markers were further increased to favor the anticancer effects of PAX in DBTRG cells in combination with RESV. The PAX and RESV-mediated increase in current density and Ca²⁺ florescence intensity was decreased with a TRPM2 blocker. This suggests that for this combination therapy to have a substantial effect on apoptosis and cell viability, the TRPM2 channel must be stimulated.

A promising redox cycle-based strategy for designing a catechol-type diphenylbutadiene as a potent prooxidative anti-melanoma agent

Developing anti-melanoma agents with increased activity and specificity is highly desirable due to the increasing incidence, highly metastatic malignancy, and high mortality rate of melanoma. Abnormal redox characteristics such as higher levels of tyrosinase, NAD(P)H: quinone oxidoreductase-1 (NQO1) and reactive oxygen species (ROS) observed in melanoma cells than in other cancer cells and normal cells illustrate their redox vulnerability and have opened a window for developing prooxidative anti-melanoma agents (PAAs) to target the vulnerability. However, how to design PAAs which promote selectively the ROS accumulation in melanoma cells remains a challenge. This work describes a promising redox cycle-based strategy for designing a catechol-type diphenylbutadiene as such type of PAA. This molecule is capable of constructing an efficient catalytic redox cycle with tyrosinase and NQO1 in melanoma B16F1 cells to induce selectively the ROS (mainly including hydrogen peroxide, H₂O₂) accumulation in the cells, resulting in highly selective suppression of melanoma B16F1 cells over tyrosinase-deficient HeLa and normal L-02 cells.