Hydroxyethyl disulfide as an efficient metabolic assay for cell viability in vitro

Targeting the Melanocortin 1 Receptor in Melanoma: Biological Activity of α-MSH-Peptide Conjugates

Malignant melanoma is one of the most aggressive and resistant tumor types, with high metastatic properties. Because of the lack of suitable chemotherapeutic agents for treatment, the 5-year survival rate of melanoma patients with regional and distant metastases is lower than 10%. Targeted tumor therapy that provides several promising results might be a good option for the treatment of malignant melanomas. Our goal was to develop novel melanoma-specific peptide-drug conjugates for targeted tumor therapy. Melanocortin-1-receptor (MC1R) is a cell surface receptor responsible for melanogenesis and it is overexpressed on the surface of melanoma cells, providing a good target. Its native ligand, α-MSH (α-melanocyte-stimulating hormone) peptide, or its derivatives, might be potential homing devices for this purpose. Therefore, we prepared three α-MSH derivative-daunomycin (Dau) conjugates and their in vitro and in vivo antitumor activities were compared. Dau has an autofluorescence property; therefore, it is suitable for preparing conjugates for in vitro (e.g., cellular uptake) and in vivo experiments. Dau was attached to the peptides via a non-cleavable oxime linkage that was applied efficiently in our previous experiments, resulting in conjugates with high tumor growth inhibition activity. The results indicated that the most promising conjugate was the compound in which Dau was connected to the side chain of Lys (Ac-SYSNleEHFRWGK(Dau=Aoa)PV-NH2). The highest cellular uptake by melanoma cells was demonstrated using the compound, with the highest tumor growth inhibition detected both on mouse (38.6% on B16) and human uveal melanoma (55% on OMC-1) cells. The effect of the compound was more pronounced than that of the free drug.

Variation in pentose phosphate pathway-associated metabolism dictates cytotoxicity outcomes determined by tetrazolium reduction assays

Tetrazolium reduction and resazurin assays are the mainstay of routine in vitro toxicity batteries. However, potentially erroneous characterization of cytotoxicity and cell proliferation can arise if verification of baseline interaction of test article with method employed is neglected. The current investigation aimed to demonstrate how interpretation of results from several standard cytotoxicity and proliferation assays vary in dependence on contributions from the pentose phosphate pathway (PPP). Non-tumorigenic Beas-2B cells were treated with graded concentrations of benzo[a]pyrene (B[a]P) for 24 and 48 h prior to cytotoxicity and proliferation assessment with commonly used MTT, MTS, WST1, and Alamar Blue assays. B[a]P caused enhanced metabolism of each dye assessed despite reductions in mitochondrial membrane potential and was reversed by 6-aminonicotinamide (6AN)-a glucose-6-phosphate dehydrogenase inhibitor. These results demonstrate differential sensitivity of standard cytotoxicity assessments on the PPP, thus (1) decoupling "mitochondrial activity" as an interpretation of cellular formazan and Alamar Blue metabolism, and (2) demonstrating the implicit requirement for investigators to sufficiently verify interaction of these methods in routine cytotoxicity and proliferation characterization. The nuances of method-specific extramitochondrial metabolism must be scrutinized to properly qualify specific endpoints employed, particularly under the circumstances of metabolic reprogramming.

Wnt-C59 inhibits proinflammatory cytokine expression by reducing the interaction between β-catenin and NF-κB in LPS-stimulated epithelial and macrophage cells

Dysregulation of the Wnt pathway causes various diseases including cancer, Parkinson’s disease, Alzheimer’s disease, schizophrenia, osteoporosis, obesity and chronic kidney diseases. The modulation of dysregulated Wnt pathway is absolutely necessary. In the present study, we evaluated the anti-inflammatory effect and the mechanism of action of Wnt-C59, a Wnt signaling inhibitor, in lipopolysaccharide (LPS)-stimulated epithelial cells and macrophage cells. Wnt-C59 showed a dose-dependent anti-inflammatory effect by suppressing the expression of proinflammatory cytokines including IL6, CCL2, IL1A, IL1B, and TNF in LPS-stimulated cells. The dysregulation of the Wnt/β-catenin pathway in LPS stimulated cells was suppressed by Wnt-C59 treatment. The level of β-catenin, the executor protein of Wnt/β-catenin pathway, was elevated by LPS and suppressed by Wnt-C59. Overexpression of β-catenin rescued the suppressive effect of Wnt-C59 on proinflammatory cytokine expression and nuclear factor-kappa B (NF-κB) activity. We found that the interaction between β-catenin and NF-κB, measured by co-immunoprecipitation assay, was elevated by LPS and suppressed by Wnt-C59 treatment. Both NF-κB activity for its target DNA binding and the reporter activity of NF-κB-responsive promoter showed identical patterns with the interaction between β-catenin and NF-κB. Altogether, our findings suggest that the anti-inflammatory effect of Wnt-C59 is mediated by the reduction of the cellular level of β-catenin and the interaction between β-catenin and NF-κB, which results in the suppressions of the NF-κB activity and proinflammatory cytokine expression.

XAV939, a Wnt/β-catenin pathway modulator, has inhibitory effects on LPS-induced inflammatory response

Aim: In this study, we report the anti-inflammatory activity of XAV939, a modulator of the Wnt/β-catenin pathway. Methods: WNT/β-catenin pathway and NF-κB signaling pathway were examined in LPS-stimulated human bronchial epithelial cells and effects of XAV939 on these pathways were analyzed. The effect of XAV939 was confirmed in human umbilical vein endothelial cells. Results: LPS-induced expressions of pro-inflammatory genes IL-6, IL-8, TNF-α, IL-1β, MCP-1, MMP-9, iNOS and COX-2 were significantly and dose-dependently suppressed by XAV939. LPS-induced NF-κB signaling, such as IκB phosphorylation and degradation as well as nuclear translocation of NF-κB, was also suppressed by XAV939. Target DNA binding of NF-κB was significantly and dose-dependently suppressed by XAV939 during LPS-induced inflammatory response. The suppressive effects of XAV939 on NF-κB signaling, target DNA binding of NF-κB and pro-inflammatory gene expression were all rescued by over expression of β-catenin, which shows that the anti-inflammatory effect of XAV939 is mediated by the modulation of β-catenin, a central component of the WNT/β-catenin pathway. Conclusion: The findings of this study showed that XAV939 exerts anti-inflammatory effects through the modulation of the Wnt/β-catenin pathway.

Comparison of specific expression profile in two in vitro hypoxia models

The microenvironment plays a fundamental role in carcinogenesis: Acidity and hypoxia are actively involved in this process. It is important to have in vitro models to study these mechanisms. The models that are most commonly referred to are the hypoxia chamber and the chemical induction [Cobalt (II) chloride]. It is not yet defined if these models are interchangeable if the metabolic effect is the same, and if the results may be compared in these models. In the present study, the response to the effect of stress (hypoxia and acidity) in both models was evaluated. The results indicated that in the chemical model, the effect of hypoxia appeared in an early form at 6 h; whereas in the gas chamber the effect was slow and gradual and at 72 h there was an overexpression of erythropoietin (EPO), vascular endothelial growth factor (VEGF), carbonic anhydrase 9 (CA9) and hypoxia-inducible factor 1α (HIF1α). In addition to the genes analyzed by reverse transcription-quantitative polymerase chain reaction, the global expression analysis between both models revealed the 9 most affected genes in common. The present study additionally identified 3 potential genes (lysyl oxidase, ankyrin repeat domain 37, B-cell lymphoma 2 interacting protein 3 like) previously identified in other studies, which may be considered as universal hypoxia genes along with HIF1α, EPO, VEGF, glucose transporter 1 (GLUT1), CA9, and LDH. To the best of the author's knowledge, this is the first time that both hypoxia models have been compared, and it was demonstrated that the effect of hypoxia induction was time sensitive in each model. These observations must be considered prior to selecting one of these models to identify selective hypoxia genes and their effects in cancer.

Gangjihwan, a polyherbal composition, inhibits fat accumulation through the modulation of lipogenic transcription factors SREBP1C, PPARγ and C/EBPα

ETHNOPHARMACOLOGICAL RELEVANCE

Gangjihwan (DF) which is composed of Ephedra intermedia, Lithospermum erythrorhizon, and Rheum palmatum has been used for the treatment of obesity in traditional medical clinics in Korea.

AIM OF THE STUDY

This study was conducted to standardize DF and elucidate its mechanism of action for inhibiting fat accumulation in adipocytes and adipose tissues.

MATERIALS AND METHODS

The herbal ingredients of DF were extracted in water, 30% ethanol or 70% ethanol and freeze-dried followed by HPLC analyses. 3T3-L1 adipocytes and high-fat diet-induced obese mice were treated with each of the three DF preparations. Messenger RNA and protein expression levels were measured by real-time qPCR and Western blotting. RNA-Seq analyses were conducted to examine the effects of DF treatment on whole transcriptome of adipocyte.

RESULTS

(-)-Ephedrine and (+)-pseudoephedrine from E. intermedia, aloe-emodin and chrysophanol from R. palmatum and shikonin from L. erythrorhizon were identified as phytochemical components of DF. DF caused dose-dependent inhibition of fat accumulation in 3T3-L1 adipocytes. It also significantly reduced adipose tissue mass and adipocyte size in high-fat diet-induced obese mice. DF was found to down-regulate the expressions of the lipogenic transcription factors such as sterol regulatory element binding protein 1C (SREBP1C), peroxisome proliferator activated receptor gamma (PPARγ), and CCAAT/enhancer binding protein alpha (C/EBPα). Among the three preparations of DF, the 70% ethanol extract was the most effective. RNA-Seq analyses showed that DF treatment decreased the expression levels of up-regulators and increased those of down-regulators of lipogenic transcription factors.

CONCLUSIONS

DF preparations, among which 70% ethanol extract was the most effective, reduced fat accumulation in 3T3-L1 adipocytes and high-fat diet-induced obese mice through the down-regulation of lipogenic transcription factors SREBP1C, PPARγ and C/EBPα.

A calpain inhibitor protects against fractalkine production in lipopolysaccharide-treated endothelial cells

Background

Fractalkine (CX3CL1) is a chemokine with a unique CX3C motif and is produced by endothelial cells stimulated with lipopolysaccharide (LPS), tumor necrosis factor (TNF)-α, interleukin (IL)-1, and interferon-γ. There have been several reports that the caspase/calpain system is activated in endotoxemia, which leads to cellular apoptosis and acute inflammatory processes. We aimed to determine the role of the caspase/calpain system in cell viability and regulation of fractalkine production in LPS-treated endothelial cells.

Methods

Human umbilical vein endothelial cells (HUVECs) were stimulated with 0.01–100 μg/mL of LPS to determine cell viability. The changes of CX3CL1 expression were compared in control, LPS (1 μg/mL)-, IL-1α (1 μg/mL)-, and IL-1β (1 μg/mL)-treated HUVECs. Cell viability and CX3CL1 production were compared with 50 μM of inhibitors of caspase-1, caspase-3, caspase-9, and calpain in LPS-treated HUVECs.

Results

Cell viability was significantly decreased from 1 to 100 μg/mL of LPS. Cell viability was significantly restored with inhibitors of caspase-1, caspase-3, caspase-9, and calpain in LPS-treated HUVECs. The expression of CX3CL1 was highest in IL-1β-treated HUVECs. CX3CL1 production was highly inhibited with a calpain inhibitor and significantly decreased with the individual inhibitors of caspase-1, caspase-3, and caspase-9.

Conclusion

The caspase/calpain system is an important modulator of cell viability and CX3CL1 production in LPS-treated endothelial cells.

Berberine activates AMPK to suppress proteolytic processing, nuclear translocation and target DNA binding of SREBP-1c in 3T3-L1 adipocytes

AMP-activated protein kinase (AMPK) and sterol regulatory element binding protein (SREBP)‑1c are major therapeutic targets in the treatment of metabolic diseases. In the present study, the fat‑reducing mechanisms of berberine (BBR), a natural isoquinoline, was investigated by examining the AMPK‑mediated modulation of SREBP‑1c in 3T3‑L1 adipocytes. BBR activated AMPK in a dose‑ and time‑dependent manner, and increased the phosphorylation of the 125‑kDa precursor form of SREBP‑1c, which suppressed its proteolytic processing into the mature 68‑kDa form and its subsequent nuclear translocation. The binding of nuclear SREBP‑1c to its E‑box motif‑containing target DNA sequence was decreased following treatment with BBR, which led to a decrease in the expression of lipogenic genes and subsequently reduced intracellular fat accumulation. Transfection with AMPKα1 siRNA, and not control siRNA, inhibited BBR‑induced phosphorylation of the 125‑kDa SREBP‑1c, which confirmed that AMPK was responsible for phosphorylating SREBP‑1c. AMPKα1 siRNA transfection rescued the proteolytic processing, nuclear translocation and target DNA binding of SREBP‑1c that had been suppressed by BBR. In addition, BBR‑induced suppression of lipogenic gene expression and intracellular fat accumulation were rescued by AMPKα1 siRNA transfection. In conclusion, the results of the present study demonstrate that BBR activates AMPK to induce phosphorylation of SREBP‑1c, thereby suppressing proteolytic processing, nuclear translocation and target DNA binding of SREBP‑1c, which leads to a reduction in lipogenic gene expression and intracellular fat accumulation. The results of the present study indicate that BBR may be a potential candidate for the development of drugs to treat obesity.

Antimetabolite TTL-315 selectively kills glucose-deprived cancer cells and enhances responses to cytotoxic chemotherapy in preclinical models of cancer

Maintaining thiol homeostasis is an imperative for cancer cell survival in the nutrient-deprived microenvironment of solid tumors. Despite this metabolic vulnerability, a selective approach has yet to be developed to disrupt thiol homeostasis in solid tumors for therapeutic purposes. In this study, we report the identification of 2-mercaptopropionyl glycine disulfide (TTL-315) as a novel antimetabolite that blocks cell survival in a manner conditional on glucose deprivation. In the presence of glucose, TTL-315 lacks cytotoxic effects in normal cells where it is detoxified by reduction to 2-mercaptopropionyl glycine, a compound with known clinical pharmacologic and safety profiles. In several rodent models of aggressive breast, lung and skin cancers, TTL-315 blocked tumor growth and cooperated with the DNA damaging drug cisplatin to trigger tumor regression. Our results offer preclinical proof of concept for TTL-315 as a novel antimetabolite to help selectively eradicate solid tumors by exploiting the glucose-deprived conditions of the tumor microenvironment.

AMPK and SREBP-1c mediate the anti-adipogenic effect of β-hydroxyisovalerylshikonin

β-hydroxyisovalerylshikonin (β-HIVS), which is a natural naphthoquinone compound, is one of the main chemicals isolated from a therapeutic plant, Lithospermum erythrorhizon. In the present study, we demonstrated that β-HIVS inhibited the adipogenesis of 3T3-L1 cells through AMP-activated protein kinase (AMPK)-mediated modulation of sterol regulatory element binding protein (SREBP)‑1c. The anti-adipogenic effect of β-HIVS was accompanied by the increased phosphorylation of AMPK and precursor SREBP‑1c. In β-HIVS-treated 3T3-L1 cells, AMPK was activated and phosphorylated precursor SREBP‑1c, preventing the cleavage of precursor SREBP‑1c to mature SREBP‑1c. Expression of the fat-forming enzymes, acetyl-CoA carboxylase (ACC)1, fatty acid synthase (FAS) and stearoyl-CoA desaturase (SCD)1, which are transcribed by mature SREBP‑1c, were downregulated, resulting in reduced intracellular fat accumulation. The anti-adipogenic effect of β-HIVS was significantly attenuated by AMPK knockdown. Knockdown of AMPK using siRNA decreased the phosphorylation of precursor SREBP‑1c and increased the levels of mature SREBP. The levels of the fat-forming enzymes, ACC1, FAS and SCD1, as well as intracellular fat accumulation were also significantly increased by AMPK knockdown. These results suggest that β-HIVS activated AMPK, which was followed by the downregulation of mature SREBP‑1c and fat-forming enzymes, leading to the inhibition of adipogenesis.

A high-performance liquid chromatography-based assay of glutathione transferase omega 1 supported by glutathione or non-physiological reductants

The unusual glutathione S-transferase GSTO1 reduces, rather than conjugates, endo- and xenobiotics, and its role in diverse cellular processes has been proposed. GSTO1 has been assayed spectrophotometrically by measuring the disappearance of its substrate, S-(4-nitrophenacyl)glutathione (4-NPG), in the presence of 2-mercaptoethanol that regenerates GSTO1 from its mixed disulfide. To assay GSTO1 in rat liver cytosol, we have developed a high-performance liquid chromatography (HPLC)-based procedure with two main advantages: (i) it measures the formation of the 4-NPG reduction product 4-nitroacetophenone, thereby offering improved sensitivity and accuracy, and (ii) it can use glutathione, the physiological reductant of GSTO1, which is impossible to do with the spectrophotometric procedure. Using the new assay, we show that (i) the GSTO1-catalyzed reduction of 4-NPG in rat liver cytosol also yields 1-(4-nitrophenyl)ethanol, whose formation from 4-nitroacetophenone requires NAD(P)H; (ii) the two assays measure comparable activities with 2-mercaptoethanol or tris(2-carboxyethyl)phosphine used as reductant; (iii) the cytosolic reduction of 4-NPG is inhibited by GSTO1 inhibitors (KT53, 5-chloromethylfluorescein diacetate, and zinc), although the inhibitory effect is strikingly influenced by the type of reductant in the assay and by the sequence of reductant and inhibitor addition. Characterization of GSTO1 inhibitors with the improved assay provides better understanding of interaction of these chemicals with the enzyme.

Real-time cell analysis: sensitivity of different vertebrate cell cultures to copper sulfate measured by xCELLigence(®)

In this study, we report the use of a real-time cell analysis (RTCA) test system, the xCELLigence(®) RTCA, as efficient tool for a fast cytotoxicity analysis and comparison of four different vertebrate cell cultures. This new dynamic real-time monitoring and impedance-based assay allows for a combined measurement of cell adhesion, spreading and proliferation. Cell cultures were obtained from mouse, rat, human and fish, all displaying a fibroblast-like phenotype. The measured impedance values could be correlated to characteristic cell culture behaviours. In parallel, relative cytotoxicity of a commonly used but due to its very good water solubility highly hazardous pesticide, copper sulfate, was evaluated under in vitro conditions through measurements of cell viability by classical end-point based assays MTT and PrestoBlue(®). Cell line responses in terms of viability as measured by these three methods were variable between the fish skin cells and cells from higher vertebrates and also between the three methods. The advantage of impedance-based measurements is mainly based on the continuous monitoring of cell responses for a broad range of different cells, including fish cells.

A bioactive probe for glutathione-dependent antioxidant capacity in breast cancer patients: implications in measuring biological effects of arsenic compounds

INTRODUCTION

Glutathione, a major cellular non-protein thiol (NPSH), serves a central role in repairing damage induced by cancer drugs, pollutants and radiation and in the detoxification of several cancer chemotherapeutic drugs and toxins. Current methods measure glutathione levels only, which require cellular extraction, rather than the glutathione recycling dependent antioxidant activity in intact cells. Here, we present a novel method using a bioactive probe of the oxidative pentose phosphate cycle, termed the OxPhos™ test, to quantify glutathione recycling dependent antioxidant activity in whole blood and intact human and rodent cells without the need for the isolation and cytoplasm extraction of cells.

METHODS

OxPhos™ test kit (Rockland Immunochemicals, USA), which uses hydroxyethyldisulfide (HEDS) as a probe for the oxidative pentose phosphate cycle, was used in these studies. The results with OxPhos™ test kit in human blood and intact cells were compared with total thiol and high pressure liquid chromatography/electrochemical detection of HEDS metabolism.

RESULTS

The OxPhos™ test measured glutathione-dependent antioxidant activity both in intact human and rodent cells and breast cancer patient's blood with a better correlation coefficient and biological variability than the thiol assay. Additionally, human blood and mammalian cells treated with various arsenicals showed a concentration-dependent decrease in activity.

DISCUSSION

The results demonstrate the application of this test for measuring the antioxidant capacity of blood and the effects of environmental pollutants/toxins. It opens up new avenues for an easy and reliable assessment of glutathione-dependent antioxidant capacity in various diseases such as stroke, blood borne diseases, infection, cardiovascular disease and other oxidative stress related diseases and as a prognostic indicator of chemotherapy response and toxicity. The use of this approach in pharmacology/toxicology including screening drugs that improve the glutathione-dependent antioxidant capacity and not just the glutathione level is clinically relevant since mammalian cells require glutathione dependent pathways for antioxidant activity.

A bioactive probe of the oxidative pentose phosphate cycle: novel strategy to reverse radioresistance in glucose deprived human colon cancer cells

The specific effects of glucose deprivation on oxidative pentose phosphate cycle (OPPC) function, thiol homeostasis, protein function and cell survival remain unclear due to lack of a glucose-sensitive chemical probe. Using p53 wild type and mutant human colon cells, we determined the effects of hydroxyethyl disulfide (HEDS) on NADPH, GSH, GSSG, total glutathione, total non-protein and protein thiol levels, the function of the DNA repair protein Ku, and the susceptibility to radiation-induced free radicals under normal glucose or glucose-deprived conditions. HEDS is rapidly detoxified in normal glucose but triggered a p53-independent metabolic stress in glucose depleted state that caused loss of NADPH, protein and non-protein thiol homeostasis and Ku function, and enhanced sensitivity of both p53 wild type and mutant cells to radiation induced oxidative stress. Additionally, high concentration of HEDS alone induced cell death in p53 wild type cells without significant effect on p53 mutant cells. HEDS offers a useful tool to gain insights into how glucose metabolism affects OPPC dependent stress-induced cellular functions and injury, including in tumor cells, where our findings imply a novel therapeutic approach to target glucose deprived tumor. Our work introduces a novel probe to address cancer metabolism and ischemic pathology.