Violacein cytotoxicity on human blood lymphocytes and effect on phosphatases

Antitumor activity of natural pigment violacein against osteosarcoma and rhabdomyosarcoma cell lines

PURPOSE

Sarcomas are rare and heterogenic tumors with unclear etiology. They develop in bone and connective tissue, mainly in pediatric patients. To increase efficacy of current therapeutic options, natural products showing selective toxicity to tumor cells are extensively investigated. Here, we evaluated antitumor activity of bacterial pigment violacein in osteosarcoma (OS) and rhabdomyosarcoma (RMS) cell lines.

METHODS

The toxicity of violacein was assessed in vitro and in vivo, using MTT assay and FET test. The effect of violacein on cell migration was monitored by wound healing assay, cell death by flow cytometry, uptake of violacein by fluorescence microscopy, generation of reactive oxygen species (ROS) by DCFH-DA assay and lipid peroxidation by TBARS assay.

RESULTS

Violacein IC50 values for OS and RMS cells were in a range from 0.35 to 0.88 µM. Its selectivity toward malignant phenotype was confirmed on non-cancer V79-4 cells, and it was safe in vivo, for zebrafish embryos in doses up to 1 µM. Violacein induced apoptosis and affected the migratory potential of OS and RMS cells. It was found on the surfaces of tested cells. Regarding the mechanism of action, violacein acted on OS and RMS cells independently of oxidative signaling, as judged by no increase in intracellular ROS generation and no lipid peroxidation.

CONCLUSION

Our study provided further evidence that reinforces the potential of violacein as an anticancer agent and candidate to consider for improvement of the effectiveness of traditional OS and RMS therapies.

Microbial synthesis of violacein pigment and its potential applications

Violacein is a pigment synthesized by Gram-negative bacteria such as Chromobacterium violaceum. It has garnered significant interest owing to its unique physiological and biological activities along with its synergistic effects with various antibiotics. In addition to C. violaceum, several microorganisms, including: Duganella sp., Pseudoalteromonas sp., Iodobacter sp., and Massilia sp., are known to produce violacein. Along with the identification of violacein-producing strains, the genetic regulation, quorum sensing mechanism, and sequence of the vio-operon involved in the biosynthesis of violacein have been elucidated. From an engineering perspective, the heterologous production of violacein using the genetically engineered Escherichia coli or Citrobacter freundii host has also been attempted. Genetic engineering of host cells involves the heterologous expression of genes involved in the vio operon and the optimization of metabolic pathways and gene regulation. Further, the crystallography of VioD and VioE was revealed, and mass production by enzyme engineering has been accelerated. In this review, we highlight the biologically assisted end-use applications of violacein (such as functional fabric development, nanoparticles, functional polymer composites, and sunscreen ingredients) and violacein activation mechanisms, production strains, and the results of mass production with engineered methods. The prospects for violacein research and engineering applications have also been discussed.

Action and function of Chromobacterium violaceum in health and disease: Violacein as a promising metabolite to counteract gastroenterological diseases

Chromobacterium violaceum is a Gram negative, β-proteobacterium found in the microbiota of tropical and subtropical environments. Although considered an opportunistic pathogen, infection rapidly progress to fatal sepsis, with metastatic abscesses. It is noteworthy the multidrug resistant phenotype of C. violaceum and the possibility of relapse. Recently, an influence of global climate in the incidence of cases beyond the previous areas has been observed. Furthermore, chronic granulomatous disease has been considered a risk factor to infection. Despite the increase in C. violaceum infection incidence and high mortality, most clinicians are not familiar with it. This review pointed out important features of this life threatening microorganism, including its pathogenicity, mechanistic aspects, genetic and drug resistance associated factors, and the clinical association with chronic granulomatous disease. In addition, its main metabolite violacein may be a promising agent to counteract gastroenterological diseases, such as colorectal cancer and inflammatory gastric lesions.

Advances in Chromobacterium violaceum and properties of violacein-Its main secondary metabolite: A review

Chromobacterium violaceum is important in the production of violacein, like other bacteria, such as Alteromonas, Janthinobacterium, Pseudoalteromonas, Duganella, Collimonas and Escherichia. Violacein is a versatile pigment, where it exhibits several biological activities, and every year, it shows increasing commercially interesting uses, especially for industrial applications in cosmetics, medicines and fabrics. This review on violacein focuses mainly on the last five years of research regarding this target compound and describes production and importance of quorum sensing in C. violaceum, mechanistic aspects of its biosynthesis, monitoring processes, genetic perspectives, pathogenic effects, antiparasitic and antimicrobial activities, immunomodulatory potential and uses, antitumor potential and industrial applications.

Violacein induces cell death by triggering mitochondrial membrane hyperpolarization in vitro

Background

Violacein is a purple pigment from Chromobacterium violaceum that possesses diverse biological and pharmacological properties. Among these, pro-oxidant and antioxidant activities have been suggested. However, the cytotoxic mechanisms induced by violacein are poorly understood and the improvement in knowledge regarding these cell death mechanisms will be useful to develop new therapeutic approaches. Considering this, in our work, we investigated the pro-oxidant effects of violacein in non-tumor (CHO-K1 and MRC-5) and tumor (HeLa) cell lines, searching for a better understanding of reactive oxygen species (ROS) production and cell death induction.

Results

Cytotoxicity induced by violacein was observed in the three cell lines; however, MRC-5 and HeLa cells were shown to be more sensitive to violacein treatment. Although punctual alterations in the antioxidant apparatus and increase in oxidative stress biomarkers was observed in some violacein concentrations, no association was found between increased oxidative stress and induction of cell death. However, the increase of mitochondrial membrane potential was observed.

Conclusions

In fact, the increase of mitochondrial membrane potential in MRC-5 and HeLa cells suggests that mitochondrial membrane hyperpolarization might be the main cause of cell death triggered by violacein.

Towards an understanding of bacterial metabolites prodigiosin and violacein and their potential for use in commercial sunscreens

OBJECTIVES

To exploit the microbial ecology of bacterial metabolite production and, specifically, to: (i) evaluate the potential use of the pigments prodigiosin and violacein as additives to commercial sunscreens for protection of human skin, and (ii) determine antioxidant and antimicrobial activities (against pathogenic bacteria) for these two pigments.

METHODS

Prodigiosin and violacein were used to supplement extracts of Aloe vera leaf and Cucumis sativus (cucumber) fruit which are known to have photoprotective activity, as well as some commercial sunscreen preparations. For each, sunscreen protection factors (SPFs) were determined spectrophotometrically. Assays for antimicrobial activity were carried out using 96-well plates to quantify growth inhibition of Staphylococcus aureus and Escherichia coli.

RESULTS

For the plant extracts, SPFs were increased by an order of magnitude (i.e. up to ~3.5) and those for the commercial sunscreens increased by 10-22% (for 4% w/w violacein) and 20-65% (for 4% w/w prodigiosin). The antioxidant activities of prodigiosin and violacein were approximately 30% and 20% those of ascorbic acid (a well-characterized, potent antioxidant). Violacein inhibited S. aureus (IC50 6.99 ± 0.146 μM) but not E. coli, whereas prodigiosin was effective against both of these bacteria (IC50 values were 0.68 ± 0.06 μM and 0.53 ± 0.03 μM, respectively).

CONCLUSION

The bacterial pigments prodigiosin and violacein exhibited antioxidant and antimicrobial activities and were able to increase the SPF of commercial sunscreens as well as the extracts of the two plant species tested. These pigments have potential as ingredients for a new product range of and, indeed, represent a new paradigm for sunscreens that utilize substances of biological origin. We discussed the biotechnological potential of these bacterial metabolites for use in commercial sunscreens, and the need for studies of mammalian cells to determine safety.

The Janthinobacterium sp. HH01 genome encodes a homologue of the V. cholerae CqsA and L. pneumophila LqsA autoinducer synthases

Janthinobacteria commonly form biofilms on eukaryotic hosts and are known to synthesize antibacterial and antifungal compounds. Janthinobacterium sp. HH01 was recently isolated from an aquatic environment and its genome sequence was established. The genome consists of a single chromosome and reveals a size of 7.10 Mb, being the largest janthinobacterial genome so far known. Approximately 80% of the 5,980 coding sequences (CDSs) present in the HH01 genome could be assigned putative functions. The genome encodes a wealth of secretory functions and several large clusters for polyketide biosynthesis. HH01 also encodes a remarkable number of proteins involved in resistance to drugs or heavy metals. Interestingly, the genome of HH01 apparently lacks the N-acylhomoserine lactone (AHL)-dependent signaling system and the AI-2-dependent quorum sensing regulatory circuit. Instead it encodes a homologue of the Legionella- and Vibrio-like autoinducer (lqsA/cqsA) synthase gene which we designated jqsA. The jqsA gene is linked to a cognate sensor kinase (jqsS) which is flanked by the response regulator jqsR. Here we show that a jqsA deletion has strong impact on the violacein biosynthesis in Janthinobacterium sp. HH01 and that a jqsA deletion mutant can be functionally complemented with the V. cholerae cqsA and the L. pneumophila lqsA genes.

Pathway redesign for deoxyviolacein biosynthesis in Citrobacter freundii and characterization of this pigment

Violacein (Vio) is an important purple pigment with many potential bioactivities. Deoxyviolacein, a structural analog of Vio, is always synthesized in low concentrations with Vio in wild-type bacteria. Due to deoxyviolacein's low production and difficulties in isolation and purification, little has been learned regarding its function and potential applications. This study was the first effort in developing a stable and efficient biosynthetic system for producing pure deoxyviolacein. A recombinant plasmid with vioabce genes was constructed by splicing using an overlapping extension-polymerase chain reaction, based on the Vio-synthesizing gene cluster of vioabcde, originating from Duganella sp. B2, and was introduced into Citrobacter freundii. With the viod gene disrupted in the Vio synthetic pathway, Vio production was completely abolished and the recombinant C. freundii synthesized only deoxyviolacein. Interestingly, vioe gene expression was strongly stimulated in the viod-deleted recombinant strain, indicating that viod disruptions could potentially induce polar effects upon the downstream vioe gene within this small operon. Deoxyviolacein production by this strain reached 1.9 g/L in shaker flasks. The product exhibited significant acid/alkali and UV resistance as well as significant inhibition of hepatocellular carcinoma cell proliferation at low concentrations of 0.1-1 μM. These physical characteristics and antitumor activities of deoxyviolacein contribute to illuminating its potential applications.

Bioactive pigments from marine bacteria: applications and physiological roles

Research into natural products from the marine environment, including microorganisms, has rapidly increased over the past two decades. Despite the enormous difficulty in isolating and harvesting marine bacteria, microbial metabolites are increasingly attractive to science because of their broad-ranging pharmacological activities, especially those with unique color pigments. This current review paper gives an overview of the pigmented natural compounds isolated from bacteria of marine origin, based on accumulated data in the literature. We review the biological activities of marine compounds, including recent advances in the study of pharmacological effects and other commercial applications, in addition to the biosynthesis and physiological roles of associated pigments. Chemical structures of the bioactive compounds discussed are also presented.

Growth inhibition and pro-apoptotic activity of violacein in Ehrlich ascites tumor

The continuing threat to biodiversity lends urgency to the need of identification of sustainable source of natural products. This is not so much trouble if there is a microbial source of the compound. Herein, violacein, a natural indolic pigment extracted from Chromobacterium violaceum, was evaluated for its antitumoral potential against the Ehrlich ascites tumor (EAT) in vivo and in vitro. Evaluation of violacein cytotoxicity using different endpoints indicated that EAT cells were twofold (IC(50)=5.0 microM) more sensitive to the compound than normal human peripheral blood lymphocytes. In vitro studies indicated that violacein cytotoxicity to EAT cells is mediated by a rapid (8-12h) production of reactive oxygen species (ROS) and a decrease in intracellular GSH levels, probably due to oxidative stress. Additionally, apoptosis was primarily induced, as demonstrated by an increase in Annexin-V positive cells, concurrently with increased levels of DNA fragmentation and increased caspase-2, caspase-9 and caspase-3 activities up to 4.5-, 6.0- and 5.5-fold, respectively, after 72 h of treatment. Moreover, doses of 0.1 and 1.0 microg kg(-1) violacein, administered intraperitoneally (i.p.) to EAT-bearing mice throughout the lifespan of the animals significantly inhibited tumor growth and increased survival of mice. In view of these results, a 35-day toxicity study was conducted in vivo. Complete hematology, biochemistry (ALT, AST and creatinine levels) and histopathological analysis of liver and kidney indicated that daily doses of violacein up to 1000 microg kg(-1) for 35 days are well tolerated and did not cause hematotoxicity nor renal or hepatotoxicity when administered i.p. to mice. Altogether, these results indicate that violacein causes oxidative stress and an imbalance in the antioxidant defense machinery of cells culminating in apoptotic cell death. Furthermore, this is the first report of its antitumor activity in vivo, which occurs in the absence of toxicity to major organs.

Growth inhibitory activity of a novel lectin from Cliona varians against K562 human erythroleukemia cells

PURPOSE

In this study, the antitumoral potential of a novel lectin (CvL) purified from the marine sponge Cliona varians was studied in different cancer cell lines.

METHODS

CvL cytotoxicity was evaluated in mammalian tumor cells and in normal human peripheral blood lymphocytes by the MTT assay using the same range of concentrations (1-150 microg ml(-1)). The mechanisms involved in K562 cell death were investigated by confocal fluorescence microscopy, flow cytometry and immunoblot.

RESULTS

CvL inhibited the growth of human leukemia cells, with IC(50) values of 70 and 100 microg ml(-1) for K562 and JURKAT cells, respectively, but it was ineffective on blood lymphocytes and solid tumor cell lines. K562 cell death occurred 72 h after exposure to the lectin and with signs of apoptosis, as analyzed by DAPI and annexin V/PI staining. Investigation of the possible mediators of this process showed that cell death occurred via a caspase-independent pathway. Confocal fluorescence microscopy indicated a pivotal role for the lysosomal protease cathepsin B in mediating cell death. Accordingly, pre-incubation of K562 cells with the cathepsin inhibitor L-trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64) abolished CvL cytotoxic effect. Furthermore, we found upregulation of tumor necrosis factor receptor 1 (TNFR1) and down-modulation of p65 subunit of nuclear factor kappa B (NFkappaB) expression in CvL-treated cells. These effects were accompanied by increased levels of p21 and reduced expression of pRb, suggesting that CvL can induce cell cycle arrest.

CONCLUSIONS

Collectively, these findings indicate an antileukemic effect for CvL and suggest that cathepsin B acts as a death mediator in CvL-induced cytotoxicity possibly in an uncharacterized connection with the membrane death receptor pathway.

Phosphoprotein levels, MAPK activities and NFkappaB expression are affected by fisetin

Flavonoids, polyphenolic phytochemicals, are ubiquitous in plants and are commonly present in the human diet. They may exert diverse beneficial effects, including antioxidant and anticarcinogenic activities. The present study was designed to evaluate three biomolecules that play important roles in the apoptotic process: mitogen-activated protein kinases, protein phosphatases and NFkappaB, using HL60 cells treated with fisetin as an experimental model. Our results demonstrated that cells treated with fisetin presented high expression of NFkappaB, activation of MAPK p38 and an increase of phosphoprotein levels; inhibition of enzymes involved in redox status maintenance were also observed. Our findings reinforce the hypothesis that fisetin is likely to exert beneficial and/or toxic actions on cells not through its potential as antioxidant but rather through its modulation of protein kinase and phosphatase signaling cascades. Additionally, our results also indicate that the cellular effects of fisetin will ultimately depend on the cell type and on the extent to which they associate with the cells, either by interactions at the membrane or by uptake into the cytosol.

Natural compounds as a source of protein tyrosine phosphatase inhibitors: application to the rational design of small-molecule derivatives

Reversible phosphorylation of tyrosine residues is a key regulatory mechanism for numerous cellular events. Protein tyrosine kinases and protein tyrosine phosphatases (PTPs) have a pivotal role in regulating both normal cell physiology and pathophysiology. Accordingly, deregulated activity of both protein tyrosine kinases and PTPs is involved in the development of numerous congenitically inherited and acquired human diseases, prompting obvious pharmaceutical and academic research interest. The development of compound libraries with higher selective PTP inhibitory activity has been bolstered by the realization that many natural products have such activity and thus are interesting biologically lead compounds, which properties are widely exploited. In addition, more rational approaches have focused on the incorporation of phosphotyrosine mimetics into specific peptide templates (peptidomimetic backbones). Additional factors furthering discovery as well as therapeutic application of new bioactive molecules are the integration of functional genomics, cell biology, structural biology, drug design, molecular screening and chemical diversity. Together, all these factors will lead to new avenues to treat clinical disease based on PTP inhibition.

Cytotoxic activity of violacein in human colon cancer cells

Several studies have shown that violacein, a purple pigment extracted from Chromobacterium violaceum, is capable to induce apoptosis in a variety of cancer cells, including those leukemia cell lines. Herein, we examined the effects of violacein on reactive oxygen species (ROS) production during the apoptotic colon cancer cell death. We demonstrate that violacein mediates ROS production followed by activation of Caspase-3, release of cytochrome c, and calcium release to citosol in Caco-2 cells. Moreover, presence of ROS scavengers such as N-acetyl-cysteine (NAC) diminishes ROS cytotoxicity induced by violacein in Caco-2 cells, indicating that violacein mediates cellular critical mechanisms in the triggering of apoptotic tumor cell death. These data also imply that violacein-induced ROS are collectively key mediators of mitochondrial membrane collapse, leading to cytochrome c release, and culminating in tumor apoptosis. Unlike in Caco-2 cells, violacein was incapable of increasing ROS levels in HT29 cells, suggesting the existence of violacein cell-type specific mechanisms. Those findings bring light to the violacein cytotoxic mechanism studies, indicating that oxidative stress play a role in the violacein-induced cytotoxicity.