Involvement of NADPH oxidase-mediated generation of reactive oxygen species in the apototic cell death by capsaicin in HepG2 human hepatoma cells

Capsaicin: a spicy way in liver disease

The incidence of liver disease continues to rise, encompassing a spectrum from simple steatosis or non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH), cirrhosis and liver cancer. Dietary habits in individuals with liver disease may significantly impact the treatment and prevention of these conditions. This article examines the role of chili peppers, a common dietary component, in this context, focusing on capsaicin, the active ingredient in chili peppers. Capsaicin is an agonist of the transient receptor potential vanilloid subfamily 1 (TRPV1) and has been shown to exert protective effects on liver diseases, including liver injury, NAFLD, liver fibrosis and liver cancer. These protective effects are attributed to capsaicin's anti-oxidant, anti-inflammatory, anti-steatosis and anti-fibrosis effects. This article reviewed the different molecular mechanisms of the protective effect of capsaicin on liver diseases.

Dapagliflozin dampens liver fibrosis induced by common bile duct ligation in rats associated with the augmentation of the hepatic Sirt1/AMPK/PGC1α/FoxO1 axis

Liver fibrosis is considered an epidemic health problem due to different insults that lead to death. Dapagliflozin (DAPA), a sodium-glucose cotransporter-2 (SGLT2) inhibitor, is one of the newer anti-diabetic drugs used to manage type 2 diabetes mellitus (T2DM). DAPA exerted beneficial effects in many human and rat models due to its antioxidant, anti-inflammatory and antifibrotic activities.

AIM

Due to previously reported capabilities related to DAPA, we designed this study to clarify the beneficial role of DAPA in liver fibrosis triggered by common bile duct ligation (CBL) in male rats.

METHODS

For 14 or 28 days after CBL procedures, DAPA was administered to the rats orally at a dose of 10 mg/kg once daily. The effects of DAPA were evaluated by assaying liver enzymes, hepatic oxidant/antioxidant parameters, serum levels of tumor necrotic factor alpha (TNF-α), and AMP-activated protein kinase (AMPK). In addition, we measured the hepatic expression of fibrosis regulator-related genes along with evaluating liver histological changes.

KEY FINDINGS

DAPA successfully decreased hepatic enzymes and malondialdehyde levels, increased superoxide dismutase activity, elevated catalase levels, decreased serum levels of TNF-α, elevated serum levels of AMPK, decreased liver hydroxyproline content, upregulated Sirt1/PGC1α/FoxO1 liver gene expressions, down-regulated fibronectin-1 (Fn-1), collagen-1 genes in liver tissues, and improved the damaged liver tissues. Deteriorated biochemical parameters and histological liver insults associated with CBL were more pronounced after 28 days, but DAPA administration for 14 and 28 days showed significant improvement in most parameters and reflected positively in the histological structures of the liver.

SIGNIFICANCE

The significance of this study lies in the observation that DAPA mitigated CBL-induced liver fibrosis in rats, most likely due to its antioxidant, anti-inflammatory, and antifibrotic effects. These results suggest that DAPA's beneficial impact on liver fibrosis might be attributed to its interaction with the Sirt1/AMPK/PGC1α/FoxO1 pathway, indicating a potential mechanistic action for future exploration.

Arvanil induces ferroptosis of hepatocellular carcinoma by binding to MICU1

Hepatocellular carcinoma (HCC) is a primary liver cancer with a high mortality rate that requires research and improved treatment strategies. Chemotherapy is still one of the main methods of HCC treatment, but it may lead to drug resistance and damage to normal organs. Capsaicin, a naturally occurring active ingredient in chili peppers, has demonstrated anticancer properties in a variety of malignant tumor cell lines. However, the anti-cancer mechanism of capsaicin needs to be further explored in HCC. In this study, we utilized Arvanil, a non-stimulating synthetic capsaicin analog, in place of capsaicin. We found that Arvanil induced high mitochondrial calcium flow, which contributed to a decrease in mitochondrial membrane permeability transition pore (mPTP) opening and oxidative phosphorylation levels, ultimately triggering cellular ferroptosis by live cells in real time with a high content screening (HCS) platform and confocal microscopy. It was further confirmed by vina molecular docking and point mutation experiments that Arvanil directly binds to two amino acid sites of mitochondrial calcium uptake protein 1 (MICU1), namely Ser47 and Phe128, to trigger this process, which in turn inhibits the growth of HCC cells. In addition, it was confirmed that Arvanil enhances cisplatin chemosensitivity by inducing HCC cellular ferroptosis in vivo. In conclusion, our study suggests that Arvanil induces ferroptosis in HCC cells and is a candidate drug for the treatment of HCC.

Capsaicin binds the N-terminus of Hsp90, induces lysosomal degradation of Hsp70, and enhances the anti-tumor effects of 17-AAG (Tanespimycin)

Heat shock protein 90 (Hsp90) and its co-chaperones promote cancer, and targeting Hsp90 holds promise for cancer treatment. Most of the efforts to harness this potential have focused on targeting the Hsp90 N-terminus ATP binding site. Although newer-generation inhibitors have shown improved efficacy in aggressive cancers, induction of the cellular heat shock response (HSR) by these inhibitors is thought to limit their clinical efficacy. Therefore, Hsp90 inhibitors with novel mechanisms of action and that do not trigger the HSR would be advantageous. Here, we investigated the mechanism by which capsaicin inhibits Hsp90. Through mutagenesis, chemical modifications, and proteomic studies, we show that capsaicin binds to the N-terminus of Hsp90 and inhibits its ATPase activity. Consequently, capsaicin and its analogs inhibit Hsp90 ATPase-dependent progesterone receptor reconstitution in vitro. Capsaicin did not induce the HSR, instead, it promoted the degradation of Hsp70 through the lysosome-autophagy pathway. Remarkably, capsaicin did not induce degradation of the constitutively expressed cognate Hsc70, indicating selectivity for Hsp70. Combined treatments of capsaicin and the Hsp90 inhibitor 17-AAG improved the anti-tumor efficacy of 17-AAG in cell culture and tridimensional tumor spheroid growth assays using breast and prostate cancer models. Consistent with this, in silico docking studies revealed that capsaicin binding to the ATP binding site of Hsp90 was distinct from classical N-terminus Hsp90 inhibitors, indicating a novel mechanism of action. Collectively, these findings support the use of capsaicin as a chemical scaffold to develop novel Hsp90 N-terminus inhibitors as well as its ability to be a potential cancer co-therapeutic.

Critical Review in Designing Plant-Based Anticancer Nanoparticles against Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), accounting for 85% of liver cancer cases, continues to be the third leading cause of cancer-related deaths worldwide. Although various forms of chemotherapy and immunotherapy have been investigated in clinics, patients continue to suffer from high toxicity and undesirable side effects. Medicinal plants contain novel critical bioactives that can target multimodal oncogenic pathways; however, their clinical translation is often challenged due to poor aqueous solubility, low cellular uptake, and poor bioavailability. Nanoparticle-based drug delivery presents great opportunities in HCC therapy by increasing selectivity and transferring sufficient doses of bioactives to tumor areas with minimal damage to adjacent healthy cells. In fact, many phytochemicals encapsulated in FDA-approved nanocarriers have demonstrated the ability to modulate the tumor microenvironment. In this review, information about the mechanisms of promising plant bioactives against HCC is discussed and compared. Their benefits and risks as future nanotherapeutics are underscored. Nanocarriers that have been employed to encapsulate both pure bioactives and crude extracts for application in various HCC models are examined and compared. Finally, the current limitations in nanocarrier design, challenges related to the HCC microenvironment, and future opportunities are also discussed for the clinical translation of plant-based nanomedicines from bench to bedside.

Capsaicin inhibits cell proliferation by enhancing oxidative stress and apoptosis through SIRT1/NOX4 signaling pathways in HepG2 and HL-7702 cells

Capsaicin could suppress the proliferation of cancer cells and inhibit many biochemical pathways associated with tumorigenesis and metastasis. This study investigates the effects of capsaicin in both hepatocellular carcinoma (HepG2) and normal hepatocytes (HL-7702) via the SIRT1/NOX4 signaling pathway. After determination of cytotoxic concentrations of capsaicin on HL-7702 and HepG2 cells, we measured total oxidant status (TOS), reduced glutathione (GSH), 8-hydroxydeoxyguanosine (8-OHdG), cytochrome c (CYC), caspase3 (CASP3), Bcl-2, Bax, sirtuin1 (SIRT1), and NADPH oxidases4 (NOX4) levels. Besides this, we analyzed the messenger RNA and protein levels of SIRT1 and NOX4. We found that capsaicin increased TOS, 8-OHdG, CASP3, CYC, Bax, and NOX4 levels, and decreased Bcl-2, GSH, and SIRT1 in a concentration-dependent manner in HepG2 cells. However, especially low capsaicin concentration (128.75 µM) enhanced GSH and SIRT levels and reduced TOS, CASP3, CYC, 8-OHdG, and NOX4 levels in HL-7702 cells (p < 0.05). Interestingly, 128.75 and 172.8 µM capsaicin treatment increased SIRT1 expression levels in HL-7702 cells, resulting in an increase in GSH levels and a decrease in TOS, CYC, CAPS3, and 8-OHdG levels through NOX4 inhibition. Furthermore, we demonstrated a significant decrease in SIRT1 protein levels and an increase in NOX4 protein levels and caspase-3/-7 activities in both HL-7702 and HepG2 cells treated with 261.5 µM capsaicin. Additionally, morphological changes in HL-7702 and HepG2 cells treated with capsaicin correlated with the enhancement in oxidative burden, DNA damage, and apoptosis. Our results show that capsaicin effectively might cause higher oxidative, apoptotic, and DNA damage in HepG2 cells than in HL-7702 cells through the SIRT1/NOX4 signaling pathway.

The Effects of Capsaicin on Gastrointestinal Cancers

Gastrointestinal (GI) cancers are a group of diseases with very high positions in the ranking of cancer incidence and mortality. While they show common features regarding the molecular mechanisms involved in cancer development, organ-specific pathophysiological processes may trigger distinct signaling pathways and intricate interactions with inflammatory cells from the tumoral milieu and mediators involved in tumorigenesis. The treatment of GI cancers is a topic of increasing interest due to the severity of these diseases, their impact on the patients' survivability and quality of life, and the burden they set on the healthcare system. As the efficiency of existing drugs is hindered by chemoresistance and adverse reactions when administered in high doses, new therapies are sought, and emerging drugs, formulations, and substance synergies are the focus of a growing number of studies. A class of chemicals with great potential through anti-inflammatory, anti-oxidant, and anti-tumoral effects is phytochemicals, and capsaicin in particular is the subject of intensive research looking to validate its position in complementing cancer treatment. Our paper thoroughly reviews the available scientific evidence concerning the effects of capsaicin on major GI cancers and its interactions with the molecular pathways involved in the course of these diseases.

Stability, permeation, and cytotoxicity reduction of capsicum extract nanoparticles loaded hydrogel containing wax gourd extract

The aim of this study was to develop hydrogel loaded with capsicum extract nanoparticles and wax gourd extract for transdermal delivery of capsaicin. The addition of wax gourd extract was supposed to reduce cytotoxicity of capsaicin in capsicum extract against HaCaT keratinocyte cell line. Capsicum extract nanoparticles were prepared by solvent displacement method using hyaluronic acid as a stabilizer. The physical and chemical stability of capsicum extract nanoparticles were investigated by dynamic light scattering technique and UV-Visible spectrophotometry, respectively. Hydrogel loaded with capsicum extract nanoparticles and wax gourd fruit extract was then formulated by using Carbopol 940® as a gelling agent for transdermal delivery. The skin permeability of capsaicin from the hydrogel was evaluated by Franz diffusion cell approach. The cytotoxicity reduction of capsicum extract nanoparticles and capsicum extract nanoparticles by mixing with wax gourd extract was determined by MTT assay The results showed that capsicum extract nanoparticles exhibited an average diameter of 168.4 ± 5.3 nm with a polydispersity index and zeta potential value of 0.26 ± 0.01 and -45.7 ± 7.1 mV, respectively. After two month-storage, particle size, polydispersity index, and zeta potential values of capsicum extract nanoparticles stored at 4° C, 30° C, and 45 °C did not significantly change. The capsaicin content decreased to 78%, 71%, and 72% when stored at 4 °C, 30 °C, and 45 °C for three months, respectively. The pH values of hydrogel containing capsicum extract nanoparticles were found to be in the range of 5.58-6.05 indicating good stability. The hydrogel exhibited a pseudoplastic character. The rate of permeation flux of capsaicin from hydrogel was 7.96 µg/cm²/h. A significant increase in cell viability was observed when the cells were incubated with capsicum extract nanoparticles mixed with wax gourd, compared to capsicum extract nanoparticles alone. The wax gourd extract in the hydrogel protected HaCaT cells from capsaicin cytotoxicity, thus may provide a new approach for delivery of capsaicin to reduce cytotoxicity to skin 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.

Targeting Ca2+ Signaling in the Initiation, Promotion and Progression of Hepatocellular Carcinoma

Simple Summary

Liver cancer (hepatocellular carcinoma) is a significant health burden worldwide. It is often not detected until at an advanced stage when there are few treatment options available. Changes in calcium concentrations within liver cancer cells are essential for regulating their growth, death, and migration (metastasis). Our aim was to review published papers which have identified proteins involved in calcium signaling as potential drug targets for the treatment of liver cancer. About twenty calcium signaling proteins were identified, including those involved in regulating calcium concentrations in the cytoplasm, endoplasmic reticulum and mitochondria. A few of these have turned out to be sites of action of natural products previously known to inhibit liver cancer. More systematic studies are now needed to determine which calcium signaling proteins might be used clinically for treatment of liver cancer, especially advanced stage cancers and those resistant to inhibition by current drugs.

Abstract

Hepatocellular carcinoma (HCC) is a considerable health burden worldwide and a major contributor to cancer-related deaths. HCC is often not noticed until at an advanced stage where treatment options are limited and current systemic drugs can usually only prolong survival for a short time. Understanding the biology and pathology of HCC is a challenge, due to the cellular and anatomic complexities of the liver. While not yet fully understood, liver cancer stem cells play a central role in the initiation and progression of HCC and in resistance to drugs. There are approximately twenty Ca²⁺-signaling proteins identified as potential targets for therapeutic treatment at different stages of HCC. These potential targets include inhibition of the self-renewal properties of liver cancer stem cells; HCC initiation and promotion by hepatitis B and C and non-alcoholic fatty liver disease (principally involving reduction of reactive oxygen species); and cell proliferation, tumor growth, migration and metastasis. A few of these Ca²⁺-signaling pathways have been identified as targets for natural products previously known to reduce HCC. Promising Ca²⁺-signaling targets include voltage-operated Ca²⁺ channel proteins (liver cancer stem cells), inositol trisphosphate receptors, store-operated Ca²⁺ entry, TRP channels, sarco/endoplasmic reticulum (Ca²⁺+Mg²⁺) ATP-ase and Ca²⁺/calmodulin-dependent protein kinases. However, none of these Ca²⁺-signaling targets has been seriously studied any further than laboratory research experiments. The future application of more systematic studies, including genomics, gene expression (RNA-seq), and improved knowledge of the fundamental biology and pathology of HCC will likely reveal new Ca²⁺-signaling protein targets and consolidate priorities for those already identified.

Therapeutic potential of targeting MKK3-p38 axis with Capsaicin for Nasopharyngeal Carcinoma

Background: Capsaicin is an active compound found in plants of the Capsicum genus; it has a range of therapeutic benefits, including anti-tumor effects. Here we aimed to delineate the inhibitory effects of capsaicin on nasopharyngeal carcinoma (NPC). Methods: The anti-cancer effects of capsaicin were confirmed in NPC cell lines and xenograft mouse models, using CCK-8, clonogenic, wound-healing, transwell migration and invasion assays. Co-immunoprecipitation, western blotting and pull-down assays were used to determine the effects of capsaicin on the MKK3-p38 axis. Cell proliferation and EMT marker expression were monitored in MKK3 knockdown (KD) or over-expression NPC cell lines treated with or without capsaicin. Finally, immunohistochemistry was performed on NPC specimens from NPC patients (n = 132) and the clinical relevance was analyzed. Results: Capsaicin inhibited cell proliferation, mobility and promoted apoptosis in NPC cells. Then we found that capsaicin directly targets p38 for dephosphorylation. As such, MKK3-induced p38 activation was inhibited by capsaicin. Furthermore, we found that capsaicin-induced inhibition of cell motility was mediated by fucokinase. Xenograft models demonstrated the inhibitory effects of capsaicin treatment on NPC tumor growth in vivo, and analysis of clinical NPC samples confirmed that MKK3 phosphorylation was associated with NPC tumor growth and lymphoid node metastasis. Conclusions: The MKK3-p38 axis represents a potential therapeutic target for capsaicin. MKK3 phosphorylation might serve as a biomarker to identify NPC patients most likely to benefit from adjunctive capsaicin treatment.

The Mediterranean Diet as source of bioactive compounds with multi-targeting anti-cancer profile

Many bioactive agents have been extracted from plants or belong to functional foods and have been considered in the treatment of serious and multifactorial diseases, such as cancer. In particular, this review is focused on the anti-cancer properties owned by several natural products typically from the Mediterranean area. In some regions of the South of Italy, a lower cancer incidence has been observed. There is increasing evidence that adherence to a Mediterranean dietary pattern correlates with reduced risk of several cancer types. This could be mainly attributed to the typical lifestyle aspects of the Mediterranean diet, such as high consumption of fruit and vegetables. In this review, the main natural products of the Mediterranean area are discussed, with particular attention on their anti-cancer properties endowed with multi-target profiles.

Capsaicin: Effects on the Pathogenesis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent cancers, and to date, there have been very few drugs available that can improve survival, the most well-known being sorafenib. The pathogenesis of HCC is complex, involving multiple processes including abnormal cell and tissue regeneration, angiogenesis, genomic instability, cellular proliferation, and signaling pathway alterations. Capsaicin is a substance that holds increasingly high interest and is studied as a therapeutic option in a wide array of diseases. Several studies have investigated capsaicin roles in various stages of HCC oncogenesis. This paper aims to thoroughly detail the available information on the individual effects of capsaicin on the cellular mechanisms and pathways involved in HCC development, as well as investigate their possible cooperation and interferences. The synergistic antitumor effects of capsaicin and sorafenib are also addressed.

SIRT1 Modulators in Experimentally Induced Liver Injury

This article is directed at highlighting the involvement of the endogenous stress sensor SIRT1 (silent information regulator T1) as a possible factor involved in hepatoprotection. The selective SIRT1 modulators whether activators (STACs) or inhibitors are being tried experimentally and clinically. We discuss the modulation of SIRT1 on cytoprotection or even cytotoxicity in the liver chemically injured by hepatotoxic agents in rats, to shed light on the crosstalk between SIRT1 and its modulators. A combination of D-galactosamine and lipopolysaccharide (D-GalN/LPS) downregulated SIRT1 expression, while SIRT1 activators, SRT1720, resveratrol, and quercetin, upregulated SIRT1 and alleviated D-GalN/LPS-induced acute hepatotoxicity. Liver injury markers exhibited an inverse relationship with SIRT1 expression. However, under subchronic hepatotoxicity, quercetin decreased the significant increase in SIRT1 expression to lower levels which are still higher than normal ones and mitigated the liver-damaging effects of carbon tetrachloride. Each of these STACs was hepatoprotective and returned the conventional antioxidant enzymes to the baseline. Polyphenols tend to fine-tune SIRT1 expression towards normal in the liver of intoxicated rats in both acute and subchronic studies. Together, all these events give an impression that the cytoprotective effects of SIRT1 are exhibited within a definite range of expression. The catalytic activity of SIRT1 is important in the hepatoprotective effects of polyphenols where SIRT1 inhibitors block and the allosteric SIRT1 activators mimic the hepatoprotective effects of polyphenols. Our findings indicate that the pharmacologic modulation of SIRT1 could represent both an important move in alleviating hepatic insults and a future major step in the treatment of xenobiotic-induced hepatotoxicity.

Analyses of repeated failures in cancer therapy for solid tumors: poor tumor-selective drug delivery, low therapeutic efficacy and unsustainable costs

For over six decades reductionist approaches to cancer chemotherapies including recent immunotherapy for solid tumors produced outcome failure-rates of 90% (±5) according to governmental agencies and industry. Despite tremendous public and private funding and initial enthusiasm about missile-therapy for site-specific cancers, molecular targeting drugs for specific enzymes such as kinases or inhibitors of growth factor receptors, the outcomes are very bleak and disappointing. Major scientific reasons for repeated failures of such therapeutic approaches are attributed to reductionist approaches to research and infinite numbers of genetic mutations in chaotic molecular environment of solid tumors that are bases of drug development. Safety and efficacy of candidate drugs tested in test tubes or experimental tumor models of rats or mice are usually evaluated and approved by FDA. Cost-benefit ratios of such ‘targeted’ therapies are also far from ideal as compared with antibiotics half a century ago. Such alarming records of failure of clinical outcomes, the increased publicity for specific vaccines (e.g., HPV or flu) targeting young and old populations, along with increasing rise of cancer incidence and death created huge and unsustainable cost to the public around the globe. This article discusses a closer scientific assessment of current cancer therapeutics and vaccines. We also present future logical approaches to cancer research and therapy and vaccines.

Methylseleninic acid induces NAD(P)H:quinone oxidoreductase-1 expression through activation of NF-E2-related factor 2 in Chang liver cells

Selenium has been reported to induce the expression of some cytoprotective enzymes, which may account for its chemoprotective and chemopreventive effects. However, it remains largely unresolved whether these effects are exerted by selenium itself or mediated by its metabolite(s). In the present study, methylseleninic acid (MSeA), a monomethylated selenium, induced the expression of NAD(P)H:quinone oxidoreductase-1 (NQO-1) in human Chang liver cells. Expression of NQO-1 and other antioxidant/stress response genes is primarily regulated by the transcription factor NF-E2-related factor2 (Nrf2). Exposure of human Chang liver cells to MSeA (3 μM) increased nuclear translocation of Nrf2 and binding to antioxidant response elements. Silencing Nrf2 markedly reduced the MSeA-induced NQO-1 expression. In comparison with embryonic fibroblasts from Nrf2 wild-type mice, those from Nrf2 knockout mice failed to induce NQO-1 expression when treated with MSeA. Moreover, MSeA treatment enhanced ubiquitination of Keap1, but repressed Nrf2 ubiquitination. Pretreatment of cells with dithiothreitol abrogated the MSeA-induced NQO-1 expression, suggesting that MSeA causes Keap1 thiol modification. MSeA-induced NQO-1 upregulation was attenuated in cells harbouring the mutant Keap1 in which the cysteine 151 residue was replaced by serine. Oral administration of MSeA (1 mg/kg) by gavage to mice induced hepatic NQO-1 expression. Similar to MSeA, methylselenol generated from selenomethionine by methioninase activity induced NQO-1 expression. In conclusion, MSeA, the immediate precursor of methylselenol, upregulates the expression of NQO-1 via the Keap1-Nrf2 signaling. The above findings suggest that biological activities of selenium are dependent on the nature of the metabolites as well as the type of ingested selenium formulations.

Capsaicin: Friend or Foe in Skin Cancer and Other Related Malignancies?

Capsaicin is the main pungent in chili peppers, one of the most commonly used spices in the world; its analgesic and anti-inflammatory properties have been proven in various cultures for centuries. It is a lipophilic substance belonging to the class of vanilloids and an agonist of the transient receptor potential vanilloid 1 receptor. Taking into consideration the complex neuro-immune impact of capsaicin and the potential link between inflammation and carcinogenesis, the effect of capsaicin on muco-cutaneous cancer has aroused a growing interest. The aim of this review is to look over the most recent data regarding the connection between capsaicin and muco-cutaneous cancers, with emphasis on melanoma and muco-cutaneous squamous cell carcinoma.

Research progress of capsaicin responses to various pharmacological challenges

Capsaicin, a well known vanilloid, has shown evidence of an ample variety of biological effects which make it the target of extensive research ever since its identification. In spite of the fact that capsaicin causes health hazards in quite a few ways, yet, the verity cannot be ignored that capsaicin has several therapeutic implications. In patients with hypersensitive bladders, vesical instillation of 1 mM capsaicin markedly improved urinary frequency and urge incontinence. Again, administration of capsaicin favors an augmentation in lipid mobilization and a decrease in adipose tissue mass. Topical capsaicin cream as well decreases postsurgical neuropathic pain and is preferred by patients over a placebo among other therapies. Several in vitro studies have revealed that capsaicin results in growth arrest in some transformed cell lines. Furthermore, capsaicin has been proven to be an undeniably exciting molecule and remains a valuable drug for alleviating pain and itch. It has been recognized that capsaicinoids are the most potential agonists of capsaicin receptor (TRPV1). However, vanilloids could exert the beneficial effects not only through the receptor-dependent pathway but also through the receptor-independent one. The involvement of serotonin, neuropeptide Substance P and somatostatin in the pharmacological actions of capsaicin has been expansively investigated. Better understanding of the established TRPV1 receptor mechanism as well as exploring other possible receptor mechanism may publicize other new clinical efficacies of capsaicin. Further, clinical studies are required in several of these conditions to establish the efficacy of capsaicin.

Capsaicin inhibits proliferation and induces apoptosis in osteosarcoma cell lines via the mitogen‑activated protein kinase pathway

Capsaicin, a pungent molecular compound present in many hot peppers, exerts anticancer activities against various human cancer cell lines by inducing apoptosis. However, the effects of capsaicin on human osteosarcoma (OS) as well as the related mechanisms remain to be fully elucidated. In the present study, the anticancer effects of capsaicin on 3 human OS cell lines (MG63, 143B and HOS) were investigated. Various concentrations of capsaicin (50-300 µM) effectively decreased cell viability in all 3 OS cell lines in a dose-dependent manner. Notably, capsaicin-induced apoptosis was observed when OS cells were treated with relatively high concentrations of capsaicin (starting at 250 µM). In addition, the mitochondrial apoptotic pathway was involved in the capsaicin-induced apoptosis in the OS cells. Meanwhile, our results also indicated that at relatively low concentrations (e.g., 100 µM), capsaicin could inhibit the proliferation, decrease the colony forming ability and induce G0/G1 phase cell cycle arrest of OS cells in a dose-dependent manner. Moreover, our results revealed that the anticancer effects induced by capsaicin on OS cell lines involved multiple MAPK signaling pathways as indicated by inactivation of the ERK1/2 and p38 pathways and activation of the JNK pathway. Furthermore, the results of animal experiments showed that capsaicin inhibited tumor growth in a xenograft model of human OS. In conclusion, these results indicate that capsaicin may exert therapeutic benefits as an adjunct to current cancer therapies but not as an independent anticancer agent.

Is cancer a severe delayed hypersensitivity reaction and histamine a blueprint?

Longevity and accumulation of multiple context-dependent signaling pathways of long-standing inflammation (antigen-load or oxidative stress) are the results of decreased/altered regulation of immunity and loss of control switch mechanisms that we defined as Yin and Yang of acute inflammation or immune surveillance. Chronic inflammation is initiated by immune disruptors-induced progressive changes in physiology and function of susceptible host tissues that lead to increased immune suppression and multistep disease processes including carcinogenesis. The interrelated multiple hypotheses that are presented for the first time in this article are extension of author's earlier series of 'accidental' discoveries on the role of inflammation in developmental stages of immune dysfunction toward tumorigenesis and angiogenesis. Detailed analyses of data on chronic diseases suggest that nearly all age-associated illnesses, generally categorized as 'mild' (e.g., increased allergies), 'moderate' (e.g., hypertension, colitis, gastritis, pancreatitis, emphysema) or 'severe' (e.g., accelerated neurodegenerative and autoimmune diseases or site-specific cancers and metastasis) are variations of hypersensitivity responses of tissues that are manifested as different diseases in immune-responsive or immune-privileged tissues. Continuous release/presence of low level histamine (subclinical) in circulation could contribute to sustained oxidative stress and induction of 'mild' or 'moderate' or 'severe' (immune tsunami) immune disorders in susceptible tissues. Site-specific cancers are proposed to be 'severe' (irreversible) forms of cumulative delayed hypersensitivity responses that would induce immunological chaos in favor of tissue growth in target tissues. Shared or special features of growth from fetus development into adulthood and aging processes and carcinogenesis are briefly compared with regard to energy requirements of highly complex function of Yin and Yang. Features of Yang (growth-promoting) arm of acute inflammation during fetus and cancer growth will be compared for consuming low energy from glycolysis (Warburg effect). Growth of fetus and cancer cells under hypoxic conditions and impaired mitochondrial energy requirements of tissues including metabolism of essential branched amino acids (e.g., val, leu, isoleu) will be compared for proposing a working model for future systematic research on cancer biology, prevention and therapy. Presentation of a working model provides insightful clues into bioenergetics that are required for fetus growth (absence of external threat and lack of high energy-demands of Yin events and parasite-like survival in host), normal growth in adulthood (balance in Yin and Yang processes) or disease processes and carcinogenesis (loss of balance in Yin-Yang). Future studies require focusing on dynamics and promotion of natural/inherent balance between Yin (tumoricidal) and Yang (tumorigenic) of effective immunity that develop after birth. Lawless growth of cancerous cells and loss of cell contact inhibition could partially be due to impaired mitochondria (mitophagy) that influence metabolism of branched chain amino acids for biosynthesis of structural proteins. The author invites interested scientists with diverse expertise to provide comments, confirm, dispute and question and/or expand and collaborate on many components of the proposed working model with the goal to better understand cancer biology for future designs of cost-effective research and clinical trials and prevention of cancer. Initial events during oxidative stress-induced damages to DNA/RNA repair mechanisms and inappropriate expression of inflammatory mediators are potentially correctable, preventable or druggable, if future studies were to focus on systematic understanding of early altered immune response dynamics toward multistep chronic diseases and carcinogenesis.

Capsaicin Inhibits Multiple Bladder Cancer Cell Phenotypes by Inhibiting Tumor-Associated NADH Oxidase (tNOX) and Sirtuin1 (SIRT1)

Bladder cancer is one of the most frequent cancers among males, and its poor survival rate reflects problems with aggressiveness and chemo-resistance. Recent interest has focused on the use of chemopreventatives (nontoxic natural agents that may suppress cancer progression) to induce targeted apoptosis for cancer therapy. Capsaicin, which has anti-cancer properties, is one such agent. It is known to preferentially inhibit a tumor-associated NADH oxidase (tNOX) that is preferentially expressed in cancer/transformed cells. Here, we set out to elucidate the correlation between tNOX expression and the inhibitory effects of capsaicin in human bladder cancer cells. We showed that capsaicin downregulates tNOX expression and decreases bladder cancer cell growth by enhancing apoptosis. Moreover, capsaicin was found to reduce the expression levels of several proteins involved in cell cycle progression, in association with increases in the cell doubling time and enhanced cell cycle arrest. Capsaicin was also shown to inhibit the activation of ERK, thereby reducing the phosphorylation of paxillin and FAK, which leads to decreased cell migration. Finally, our results indicate that RNA interference-mediated tNOX depletion enhances spontaneous apoptosis, prolongs cell cycle progression, and reduces cell migration and the epithelial-mesenchymal transition. We also observed a downregulation of sirtuin 1 (SIRT1) in these tNOX-knockdown cells, a deacetylase that is important in multiple cellular functions. Taken together, our results indicate that capsaicin inhibits the growth of bladder cancer cells by inhibiting tNOX and SIRT1 and thereby reducing proliferation, attenuating migration, and prolonging cell cycle progression.

Update on a tumor-associated NADH oxidase in gastric cancer cell growth

Gastric cancer is one of the most common human malignancies, and its prevalence has been shown to be well-correlated with cancer-related deaths worldwide. Regrettably, the poor prognosis of this disease is mainly due to its late diagnosis at advanced stages after the cancer has already metastasized. Recent research has emphasized the identification of cancer biomarkers in the hope of diagnosing cancer early and designing targeted therapies to reverse cancer progression. One member of a family of growth-related nicotinamide adenine dinucleotide (NADH or hydroquinone) oxidases is tumor-associated NADH oxidase (tNOX; ENOX2). Unlike its counterpart CNOX (ENOX1), identified in normal rat liver plasma membranes and shown to be stimulated by growth factors and hormones, tNOX activity purified from rat hepatoma cells is constitutively active. Its activity is detectable in the sera of cancer patients but not in those of healthy volunteers, suggesting its clinical relevance. Interestingly, tNOX expression was shown to be present in an array of cancer cell lines. More importantly, inhibition of tNOX was well correlated with reduced cancer cell growth and induction of apoptosis. RNA interference targeting tNOX expression in cancer cells effectively restored non-cancerous phenotypes, further supporting the vital role of tNOX in cancer cells. Here, we review the regulatory role of tNOX in gastric cancer cell growth.

Capsaicin and Its Role in Chronic Diseases

A significant number of experimental and clinical studies published in peer-reviewed journals have demonstrated promising pharmacological properties of capsaicin in relieving signs and symptoms of non-communicable diseases (chronic diseases). This chapter provides an overview made from basic and clinical research studies of the potential therapeutic effects of capsaicin, loaded in different application forms, such as solution and cream, on chronic diseases (e.g. arthritis, chronic pain, functional gastrointestinal disorders and cancer). In addition to the anti-inflammatory and analgesic properties of capsaicin largely recognized via, mainly, interaction with the TRPV1, the effects of capsaicin on different cell signalling pathways will be further discussed here. The analgesic, anti-inflammatory or apoptotic effects of capsaicin show promising results in arthritis, neuropathic pain, gastrointestinal disorders or cancer, since evidence demonstrates that the oral or local application of capsaicin reduce inflammation and pain in rheumatoid arthritis, promotes gastric protection against ulcer and induces apoptosis of the tumour cells. Sadly, these results have been paralleled by conflicting studies, which indicate that high concentrations of capsaicin are likely to evoke deleterious effects, thus suggesting that capsaicin activates different pathways at different concentrations in both human and rodent tissues. Thus, to establish effective capsaicin doses for chronic conditions, which can be benefited from capsaicin therapeutic effects, is a real challenge that must be pursued.

Selective killing of K-ras-transformed pancreatic cancer cells by targeting NAD(P)H oxidase

Introduction

Oncogenic activation of the K-ras gene occurs in >90% of pancreatic ductal carcinoma and plays a critical role in the pathogenesis of this malignancy. Increase of reactive oxygen species (ROS) has also been observed in a wide spectrum of cancers. This study aimed to investigate the mechanistic association between K-ras–induced transformation and increased ROS stress and its therapeutic implications in pancreatic cancer.

Methods

ROS level, NADPH oxidase (NOX) activity and expression, and cell invasion were examined in human pancreatic duct epithelial E6E7 cells transfected with K-ras^G12V compared with parental E6E7 cells. The cytotoxic effect and antitumor effect of capsaicin, a NOX inhibitor, were also tested in vitro and in vivo.

Results

K-ras transfection caused activation of the membrane-associated redox enzyme NOX and elevated ROS generation through the phosphatidylinositol 3′-kinase (PI3K) pathway. Importantly, capsaicin preferentially inhibited the enzyme activity of NOX and induced severe ROS accumulation in K-ras–transformed cells compared with parental E6E7 cells. Furthermore, capsaicin effectively inhibited cell proliferation, prevented invasiveness of K-ras–transformed pancreatic cancer cells, and caused minimum toxicity to parental E6E7 cells. In vivo, capsaicin exhibited antitumor activity against pancreatic cancer and showed oxidative damage to the xenograft tumor cells.

Conclusions

K-ras oncogenic signaling causes increased ROS stress through NOX, and abnormal ROS stress can selectively kill tumor cells by using NOX inhibitors. Our study provides a basis for developing a novel therapeutic strategy to effectively kill K-ras–transformed cells through a redox-mediated mechanism.

Capsaicin inhibits the adipogenic differentiation of bone marrow mesenchymal stem cells by regulating cell proliferation, apoptosis, oxidative and nitrosative stress

Suppression of the maturation of pre-adipocytes into adipocytes and inhibition of the differentiation of mesenchymal stem cells into adipocytes by capsaicin.

Oxidant-based anticancer activity of a novel synthetic analogue of capsaicin, capsaicin epoxide

OBJECTIVES

Plant-derived natural substances, such as capsaicin, with potent antiproliferative activity against cancer cells in vitro are considered to be promising nutraceuticals in anticancer therapy. Nevertheless, the limited systemic bioavailability of phytochemicals may raise questions regarding the physiological relevance of their phytochemical effects in vivo. Thus, the search for novel phytochemical-based substances with more efficient anticancer action is needed.

METHODS

In the present study, a capsaicin analogue, namely, capsaicin epoxide, was synthesized, and its cytotoxic potential against cancer cells was evaluated and compared to that of capsaicin through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and multi-caspase assays. The abilities of capsaicin and capsaicin epoxide to induce oxidative stress were estimated using redox-sensitive fluorogenic probes: 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA) and dihydroethidium.

RESULTS

The structure and purity of the synthesized product were confirmed by nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and gas chromatography. Normal human dermal fibroblasts were not susceptible to treatment with the agent, whereas a cancer cell type-specific response was observed. Human breast carcinoma cells were found to be the most sensitive to capsaicin epoxide treatment compared with capsaicin treatment, and the action of capsaicin epoxide was oxidant based.

DISCUSSION

Our data indicate that the antiproliferative activity of capsaicin epoxide is potentiated in vitro, when used at much lower concentrations compared with capsaicin at similar concentrations. Thus, the findings of this study may have implications for phytochemical-based anticancer drug development.

Induction of hepatoma carcinoma cell apoptosis through activation of the JNK-nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-ROS self-driven death signal circuit

As an efficient method for inducing tumor cell apoptosis, ROS can be constantly formed and accumulated in NADPH oxidase overactivated-cells, resulting in further mitochondrial membrane damage and mitochondria-dependent apoptosis. In addition, JNK mitogen-activated protein kinase (JNK MAPK) signal also acts as a vital candidate pathway for inducing tumor cell apoptosis by targeting mitochondrial death pathway. However, the relationship between NADPH oxidase-ROS and JNK MAPK signal still remains unclear. Here, we discovered a novel self-driven signal circuit between NADPH oxidase-ROS and JNK MAPK, which was induced by a cytotoxic steroidal saponin (ASC) in hepatoma carcinoma cells. NADPH oxidase-dependent ROS production was markedly activated by ASC and directly led to JNK MAPK activation. Moreover, antioxidant, NADPH oxidase inhibitor and specific knock-out for p47 subunit of NADPH oxidase could effectively block NADPH oxidase-ROS-dependent JNK activation, suggesting that NADPH oxidase is an upstream regulator of JNK MAPK. Conversely, a specific JNK inhibitor could inhibit ASC-induced NADPH oxidase activation and down-regulate ROS levels as well, indicating that JNK might also regulate NADPH oxidase activity to some extent. These observations indicate that NADPH oxidase and JNK MAPK activate each other as a signal circuit. Furthermore, drug pretreatment experiments with ASC showed this signal circuit operated continuously via a self-driven mode and finally induced apoptosis in hepatoma carcinoma cells. Taken together, we provide a proof for inducing hepatoma carcinoma cell apoptosis by activating the JNK-NADPH oxidase-ROS-dependent self-driven signal circuit pathway.

The potential antitumor effects of capsaicin

Capsaicin, one of the major pungent ingredients found in red peppers, has been recently demonstrated to induce apoptosis in many types of malignant cell lines including colon adenocarcinoma, pancreatic cancer, hepatocellular carcinoma, prostate cancer, breast cancer, and many others. The mechanism whereby capsaicin induces apoptosis in cancer cells is not completely elucidated but involves intracellular calcium increase, reactive oxygen species generation, disruption of mitochondrial membrane transition potential, and activation of transcription factors such as NFkappaB and STATS. Recently, a role for the AMP-dependent kinase (AMPK) and autophagy pathways in capsaicin-triggered cell death has been proposed. In addition, capsaicin shows antitumor activity in vivo by reducing the growth of many tumors induced in mice. In this chapter, we report the last advances performed in the antitumor activity of capsaicin and review the main signaling pathways involved.

Capsaicin induces apoptosis in SCC-4 human tongue cancer cells through mitochondria-dependent and -independent pathways

Although there have been advances in the fields of surgery, radiotherapy, and chemotherapy of tongue cancer, the cure rates are still not substantially satisfactory. Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is the major pungent ingredient of hot chili pepper and has been reported to have an antitumor effect on many human cancer cell types. The molecular mechanisms of the antitumor effect of capsaicin are not yet completely understood. Herein, we investigated whether capsaicin induces apoptosis in human tongue cancer cells. Capsaicin decreased the percentage of viable cells in a dose-dependent manner in human tongue cancer SCC-4 cells. In addition, capsaicin produced DNA fragmentation, decreased the DNA contents (sub-G1 phase), and induced G0/G1 phase arrest in SCC-4 cells. We demonstrated that capsaicin-induced apoptosis is associated with an increase in reactive oxygen species and Ca²⁺ generations and a disruption of the mitochondrial transmenbrane potential (ΔΨ(m)). Treatment with capsaicin induced a dramatic increase in caspase-3 and -9 activities, as assessed by flow cytometric methods. A possible mechanism of capsaicin-induced apoptosis is involved in the activation of caspase-3 (one of the apoptosis-executing enzyme). Confocal laser microscope examination also showed that capsaicin induced the releases of AIF, ATF-4, and GADD153 from mitochondria of SCC-4 cells.

Production of reactive oxygen species by multipotent stromal cells/mesenchymal stem cells upon exposure to fas ligand

Multipotent stromal cells (MSCs) can be differentiated into osteoblasts and chondrocytes, making these cells candidates to regenerate cranio-facial injuries and lesions in long bones. A major problem with cell replacement therapy, however, is the loss of transplanted MSCs at the site of graft. Reactive oxygen species (ROS) and nonspecific inflammation generated at the ischemic site have been hypothesized to lead to MSCs loss; studies in vitro show MSCs dying both in the presence of ROS or cytokines like FasL. We questioned whether MSCs themselves may be the source of these death inducers, specifically whether MSCs produce ROS under cytokine challenge. On treating MSCs with FasL, we observed increased ROS production within 2 h, leading to apoptotic death after 6 h of exposure to the cytokine. N-acetyl cysteine, an antioxidant, is able to protect MSCs from FasL-induced ROS production and subsequent ROS-dependent apoptosis, though the MSCs eventually succumb to ROS-independent death signaling. Epidermal growth factor (EGF), a cell survival factor, is able to protect cells from FasL-induced ROS production initially; however, the protective effect wanes with continued FasL exposure. In parallel, FasL induces upregulation of the uncoupling protein UCP2, the main uncoupling protein in MSCs, which is not abrogated by EGF; however, the production of ROS is followed by a delayed apoptotic cell death despite moderation by UCP2. FasL-induced ROS activates the stress-induced MAPK pathways JNK and p38MAPK as well as ERK, along with the activation of Bad, a proapoptotic protein, and suppression of survivin, an antiapoptotic protein; the latter two key modulators of the mitochondrial death pathway. FasL by itself also activates its canonical extrinsic death pathway noted by a time-dependent degradation of c-FLIP and activation of caspase 8. These data suggest that MSCs participate in their own demise due to nonspecific inflammation, holding implications for replacement therapies.

Capsaicin-mediated tNOX (ENOX2) up-regulation enhances cell proliferation and migration in vitro and in vivo

Cancer chemoprevention is employed to block or reverse the progression of malignancies. To date, several thousands of agents have been found to possess chemopreventative activity, one of which is capsaicin, a component of chili peppers that exhibits antigrowth activity against various cancer cell lines. However, the role of capsaicin in tumorigenesis remains controversial because both cancer prevention and promotion have been proposed. Here, we made the unexpected discovery that treatment with low concentrations of capsaicin up-regulates tNOX (tumor-associated NADH oxidase) expression in HCT116 human colon carcinoma cells in association with enhanced cell proliferation and migration, as evidenced by down-regulation of epithelial markers and up-regulation of mesenchymal markers. Importantly, tNOX-knockdown in HCT116 cells by RNA interference reversed capsaicin-induced cell proliferation and migration in vitro and decreased tumor growth in vivo. Collectively, these findings provide a basis for explaining the tumor-promoting effect of capsaicin and might imply that caution should be taken when using capsaicin as a chemopreventive agent.

Down-regulation of tumor-associated NADH oxidase, tNOX (ENOX2), enhances capsaicin-induced inhibition of gastric cancer cell growth

Gastric cancer is a common human malignancy and a major contributor to cancer-related deaths worldwide. Unfortunately, the prognosis of most gastric cancer patients is poor because they are generally diagnosed at a late stage after the cancer has already metastasized. Most current research, therefore, emphasizes selective targeting of cancer cells by apoptosis-inducing agents. One such therapeutic agent is capsaicin, a component of chili peppers that has been shown to possess anti-growth activity against various cancer cell lines. Here, we examined the effect of capsaicin on SNU-1 and TMC-1 gastric cancer cells and found differing outcomes between the two cell lines. Our results show that capsaicin induced significant cytotoxicity with increases in oxidative stress, PARP cleavage, and apoptosis in sensitive SNU-1 cells. In contrast, TMC-1 cells were much less sensitive to capsaicin, exhibiting low cytotoxicity and very little apoptosis in response to capsaicin treatment. Capsaicin-induced apoptosis in SNU-1 cells was associated with down-regulation of tumor-associated NADH oxidase (tNOX) mRNA and protein. On the contrary, tNOX expression was scarcely affected by capsaicin in TMC-1 cells. We further showed that tNOX-knockdown sensitized TMC-1 cells to capsaicin-induced apoptosis and G1 phase accumulation, and led to decreased cell growth, demonstrating that tNOX is essential for cancer cell growth. Collectively, these results indicate that capsaicin induces divergent effects of the growth of gastric cancer cells that parallel its effects on tNOX expression, and demonstrate that forced tNOX down-regulation restored capsaicin-induced growth inhibition in TMC-1 cells.

Roles of reactive oxygen and nitrogen species in pain

Peroxynitrite (PN; ONOO⁻) and its reactive oxygen precursor superoxide (SO; O₂•⁻) are critically important in the development of pain of several etiologies including pain associated with chronic use of opiates such as morphine (also known as opiate-induced hyperalgesia and antinociceptive tolerance). This is now an emerging field in which considerable progress has been made in terms of understanding the relative contributions of SO, PN, and nitroxidative stress in pain signaling at the molecular and biochemical levels. Aggressive research in this area is poised to provide the pharmacological basis for development of novel nonnarcotic analgesics that are based upon the unique ability to selectively eliminate SO and/or PN. As we have a better understanding of the roles of SO and PN in pathophysiological settings, targeting PN may be a better therapeutic strategy than targeting SO. This is because, unlike PN, which has no currently known beneficial role, SO may play a significant role in learning and memory. Thus, the best approach may be to spare SO while directly targeting its downstream product, PN. Over the past 15 years, our team has spearheaded research concerning the roles of SO and PN in pain and these results are currently leading to the development of solid therapeutic strategies in this important area.

Capsaicin mediates apoptosis in human nasopharyngeal carcinoma NPC-TW 039 cells through mitochondrial depolarization and endoplasmic reticulum stress

Capsaicin, a pungent compound found in hot chili peppers, has been reported to have antitumor activities in many human cancer cell lines, but the induction of precise apoptosis signaling pathway in human nasopharyngeal carcinoma (NPC) cells is unclear. Here, we investigated the molecular mechanisms of capsaicin-induced apoptosis in human NPC, NPC-TW 039, cells. Effects of capsaicin involved endoplasmic reticulum (ER) stress, caspase-3 activation and mitochondrial depolarization. Capsaicin-induced cytotoxic effects (cell death) through G0/G1 phase arrest and induction of apoptosis of NPC-TW 039 cells in a dose-dependent manner. Capsaicin treatment triggered ER stress by promoting the production of reactive oxygen species (ROS), increasing levels of inositol-requiring 1 enzyme (IRE1), growth arrest and DNA-damage-inducible 153 (GADD153) and glucose-regulated protein 78 (GRP78). Other effects included an increase in cytosolic Ca(2+), loss of the mitochondrial transmembrane potential (ΔΨ(m)), releases of cytochrome c and apoptosis-inducing factor (AIF), and activation of caspase-9 and -3. Furthermore, capsaicin induced increases in the ratio of Bax/Bcl-2 and abundance of apoptosis-related protein levels. These results suggest that ER stress- and mitochondria-mediated cell death is involved in capsaicin-induced apoptosis in NPC-TW 039 cells.

Role of mitochondrial electron transport chain complexes in capsaicin mediated oxidative stress leading to apoptosis in pancreatic cancer cells

We evaluated the mechanism of capsaicin-mediated ROS generation in pancreatic cancer cells. The generation of ROS was about 4–6 fold more as compared to control and as early as 1 h after capsaicin treatment in BxPC-3 and AsPC-1 cells but not in normal HPDE-6 cells. The generation of ROS was inhibited by catalase and EUK-134. To delineate the mechanism of ROS generation, enzymatic activities of mitochondrial complex-I and complex-III were determined in the pure mitochondria. Our results shows that capsaicin inhibits about 2.5–9% and 5–20% of complex-I activity and 8–75% of complex-III activity in BxPC-3 and AsPC-1 cells respectively, which was attenuable by SOD, catalase and EUK-134. On the other hand, capsaicin treatment failed to inhibit complex-I or complex-III activities in normal HPDE-6 cells. The ATP levels were drastically suppressed by capsaicin treatment in both BxPC-3 and AsPC-1 cells and attenuated by catalase or EUK-134. Oxidation of mitochondria-specific cardiolipin was substantially higher in capsaicin treated cells. BxPC-3 derived ρ⁰ cells, which lack mitochondrial DNA, were completely resistant to capsaicin mediated ROS generation and apoptosis. Our results reveal that the release of cytochrome c and cleavage of both caspase-9 and caspase-3 due to disruption of mitochondrial membrane potential were significantly blocked by catalase and EUK-134 in BxPC-3 cells. Our results further demonstrate that capsaicin treatment not only inhibit the enzymatic activity and expression of SOD, catalase and glutathione peroxidase but also reduce glutathione level. Over-expression of catalase by transient transfection protected the cells from capsaicin-mediated ROS generation and apoptosis. Furthermore, tumors from mice orally fed with 2.5 mg/kg capsaicin show decreased SOD activity and an increase in GSSG/GSH levels as compared to controls. Taken together, our results suggest the involvement of mitochondrial complex-I and III in capsaicin-mediated ROS generation and decrease in antioxidant levels resulting in severe mitochondrial damage leading to apoptosis in pancreatic cancer cells.

Reciprocal relationship between cytosolic NADH and ENOX2 inhibition triggers sphingolipid-induced apoptosis in HeLa cells

ENOX2 (tNOX), a tumor-associated cell surface ubiquinol (NADH) oxidase, functions as an alternative terminal oxidase for plasma membrane electron transport. Ubiquitous in all cancer cell lines studied thus far, ENOX2 expression correlates with the abnormal growth and division associated with the malignant phenotype. ENOX2 has been proposed as the cellular target for various quinone site inhibitors that demonstrate anticancer activity such as the green tea constituent epigallocatechin-3-gallate (EGCg) and the isoflavone phenoxodiol (PXD). Here we present a possible mechanism that explains how these substances result in apoptosis in cancer cells by ENOX2-mediated alterations of cytosolic amounts of NAD(+) and NADH. When ENOX2 is inhibited, plasma membrane electron transport is diminished, and cytosolic NADH accumulates. We show in HeLa cells that NADH levels modulate the activities of two pivotal enzymes of sphingolipid metabolism: sphingosine kinase 1 (SK1) and neutral sphingomyelinase (nSMase). Their respective products sphingosine 1-phosphate (S1P) and ceramide (Cer) are key determinants of cell fate. S1P promotes cell survival and Cer promotes apoptosis. Using plasma membranes isolated from cervical adenocarcinoma (HeLa) cells as well as purified proteins of both bacterial and human origin, we demonstrate that NADH inhibits SK1 and stimulates nSMase, while NAD(+) inhibits nSMase and has no effect on SK1. Additionally, intact HeLa cells treated with ENOX2 inhibitors exhibit an increase in Cer and a decrease in S1P. Treatments that stimulate cytosolic NADH production potentiate the antiproliferative effects of ENOX2 inhibitors while those that attenuate NADH production or stimulate plasma membrane electron transport confer a survival advantage.

Impact of central and peripheral TRPV1 and ROS levels on proinflammatory mediators and nociceptive behavior

Background

Transient receptor potential vanilloid 1 (TRPV1) channels are important membrane sensors on peripheral nerve endings and on supportive non-neuronal synoviocytes in the knee joint. TRPV 1 ion channels respond with activation of calcium and sodium fluxes to pH, thermal, chemical, osmotic, mechanical and other stimuli abundant in inflamed joints. In the present study, the kaolin/carrageenan (k/c) induced knee joint arthritis model in rats, as well as primary and clonal human synoviocyte cultures were used to understand the reciprocal interactions between reactive nitroxidative species (ROS) and functional TRPV1 channels. ROS generation was monitored with ROS sensitive dyes using live cell imaging in vitro and in spinal tissue histology, as well as with measurement of ROS metabolites in culture media using HPLC.

Results

Functional responses in the experimental arthritis model, including increased nociceptive responses (thermal and mechanical hyperalgesia and allodynia), knee joint temperature reflecting local blood flow, and spinal cord ROS elevations were reduced by the ROS scavenger PBN after intraperitoneal pretreatment. Increases in TRPV1 and ROS, generated by synoviocytes in vitro, were reciprocally blocked by TRPV1 antagonists and the ROS scavenger. Further evidence is presented that synoviocyte responses to ROS and TRPV1 activation include increases in TNFα and COX-2, both measured as an indicator of the inflammation in vitro.

Conclusions

The results demonstrate that contributions of ROS to pronociceptive responses and neurogenic inflammation are mediated both centrally and peripherally. Responses are mediated by TRPV1 locally in the knee joint by synoviocytes, as well as by ROS-induced sensitization in the spinal cord. These findings and those of others reported in the literature indicate reciprocal interactions between TRPV1 and ROS play critical roles in the pathological and nociceptive responses active during arthritic inflammation.

Selective induction of catalase-mediated autophagy by dihydrocapsaicin in lung cell lines

We reported that dihydrocapsaicin (DHC) induces autophagy in a catalase-regulated manner. In this study, we further examined the role of DHC-induced autophagy in lung cell lines. DHC-induced cytotoxicity was higher in WI38 and H1299 cells than in H460 and A549 cells, and was related to the loss of cell membrane integrity. However, apoptotic cells markedly increased in H460 and A549 cells. In WI38 and H1299 cells, DHC-induced catalase was correlated with a decrease of intracellular reactive oxygen species (ROS) and an increase in the level of LC3II, an autophagy marker, and LC3 conversion was attenuated by the catalase inhibitor 3-amino-1,2,4-triazole (3AT) or by knockdown of the catalase gene. In A549 cells, DHC downregulated catalase, led to ROS accumulation, and blocked LC3 conversion. In H460 cells expressing limited amount of catalase, DHC caused ROS accumulation and blocked LC3 conversion. However, H460 cells overexpressing catalase were able to induce autophagy. In contrast to Earle's balanced salt solution and rotenone, H(2)O(2) treatment caused ROS accumulation and did not promote upregulation of catalase and LC3II in lung cell lines. Cytoplasmic vacuolization in WI38 and H1299 cells was blocked by treatment of 3AT and which enhanced caspase-3 activity and LDH release. Suppression of autophagy by 3-methyladenine also enhanced DHC-induced cell death through apoptotic and necrotic cell death. In A549 and H460 cells, treatment of rapamycin attenuated DHC-induced cell death. Collectively, these results suggest that catalase regulates autophagy, which helps protect cells against apoptotic and necrotic cell death.

Autophagy induction by capsaicin in malignant human breast cells is modulated by p38 and extracellular signal-regulated mitogen-activated protein kinases and retards cell death by suppressing endoplasmic reticulum stress-mediated apoptosis

In our previous study, we showed that capsaicin induces autophagy in several cell lines. Here, we investigated the molecular mechanisms of capsaicin-induced autophagy in malignant (MCF-7 and MDA-MB-231) and normal (MCF10A) human breast cells. Capsaicin caused nonapoptotic cell cycle arrest of MCF-7 and MDA-MB-231 cells but induced apoptosis in MCF10A cells. In MCF-7 and MDA-MB-231 cells, capsaicin induced endoplasmic reticulum (ER) stress via inositol-requiring 1 and Chop and induced autophagy, as demonstrated by microtubule-associated protein 1 light chain-3 (LC3) conversion. Autophagy blocking by 3-methyladenine (3MA) or bafilomycin A1 (BaF1) activated caspase-4 and -7 and enhanced cell death. In MCF-7 and MDA-MB-231 cells, p38 was activated for more than 48 h by capsaicin treatment, but extracellular signal-regulated kinase (ERK) activation decreased after 12 h, and LC3II levels continuously increased. Furthermore, treatment with 3MA markedly down-regulated capsaicin-induced p38 activation and LC3 conversion, and BaF1 completely down-regulated ERK activation and led to LC3II accumulation. In addition, pharmacological blockade or knockdown of the p38 gene down-regulated Akt activation and LC3II levels but did not affect ERK, and pharmacological blockade or knockdown of the ERK gene up-regulated LC3II induction by capsaicin. Knockdown of inositol-requiring 1 down-regulated p38-Akt signaling. In MCF10A cells, capsaicin did not elicit p38 activation and LC3 conversion and caused the sustained activation of caspase-4. Collectively, capsaicin-induced autophagy is regulated by p38 and ERK; p38 controls autophagy at the sequestration step, whereas ERK controls autophagy at the maturation step, and that autophagy is involved in the retardation of cell death by blocking capsaicin-induced ER stress-mediated apoptosis in MCF-7 and MDA-MB-321 cells.

Effect of Ccapsaicin on tNOX (ENOX2) protein expression in stomach cancer cells

Tumor-associated NADH oxidase (tNOX, also known as ENOX2) is a growth-related protein expressed in transformed cells. Previous reports have revealed that the inhibition of tNOX activity by the anti-cancer drug, capsaicin, correlates with a reduction in growth of cancer cells, indicating a close relationship between tNOX activity and cell growth. Moreover, the study of depleted tNOX expression by RNA interference in HeLa cells suggests that it may be associated with the ability of tumor cells to acquire an aggressive phenotype, particularly in relation to cell proliferation. A key role for tNOX in regulating cell growth is further supported by the observation that the growth rate of MEF cells from tNOX-overexpressing transgenic mice is approximately two-fold greater than that of wild-type cells. The purpose of this study was to investigate the anti-proliferative effect of capsaicin on tNOX expression level in stomach cancer cells. We showed that capsaicin induced cytotoxicity in SCM cells concomitantly with apoptosis, PARP cleavage, and down-regulation of tNOX protein.

Block effect of capsaicin on hERG potassium currents is enhanced by S6 mutation at Y652

The objectives of this study were to investigate the inhibitory action of capsaicin on wild-type (WT) and mutation human ether-a-go-go-related gene (hERG) potassium channel currents (I(hERG)), and to determine whether mutations in the S6 region are significant for the inhibition of I(hERG) by capsaicin. The hERG channel (WT, Y652A and F656A) was expressed in Xenopus oocytes and studied using standard two-microelectrode voltage-clamp techniques. The results show that capsaicin blocks WT hERG in a concentration-dependent manner, with an IC(50) of 17.45microM and a negative shift in the steady-state inactivation curve. Characteristics of blockade were consistent with capsaicin causing components of block in both the closed and open channel states. However, mutating the Y652 residue to Ala enhances the blockade effect of capsaicin with an IC(50) of 4.11microM, whereas mutation of F656A does not significantly alter drug potency. Simultaneously, for Y652A, the steady-state activation parameter is shifted to a more positive value by 5mV and the inactivation parameter is shifted to a more negative value by -29mV in the presence of 25microM capsaicin. In conclusion, capsaicin blocks hERG channels by binding to both the closed and open channel states.Y652 was important as a molecular determinant of blockade. Mutation Y652A enhances the drug block, which may cause some patients to be particularly sensitive to capsaicin clinically.

Capsaicin-induced apoptosis is regulated by endoplasmic reticulum stress- and calpain-mediated mitochondrial cell death pathways

Capsaicin, a pungent compound found in hot chili peppers, induces apoptotic cell death in various cell lines, however, the precise apoptosis signaling pathway is unknown. Here, we investigated capsaicin-induced apoptotic signaling in the human breast cell line MCF10A and found that it involves both endoplasmic reticulum (ER) stress and calpain activation. Capsaicin inhibited growth in a dose-dependent manner and induced apoptotic nuclear changes in MCF10A cells. Capsaicin also induced degradation of tumor suppressor p53; this effect was enhanced by the ER stressor tunicamycin. The proteasome inhibitor MG132 completely blocked capsaicin-induced p53 degradation and enhanced apoptotic cell death. Capsaicin treatment triggered ER stress by increasing levels of IRE1, GADD153/Chop, GRP78/Bip, and activated caspase-4. It led to an increase in cytosolic Ca(2+), calpain activation, loss of the mitochondrial transmembrane potential, release of mitochondrial cytochrome c, and caspase-9 and -7 activation. Furthermore, capsaicin-induced the mitochondrial apoptotic pathway through calpain-mediated Bid translocation to the mitochondria and nuclear translocation of apoptosis-inducing factor (AIF). Capsaicin-induced caspase-9, Bid cleavage, and AIF translocation were blocked by calpeptin, and BAPTA and calpeptin attenuated calpain activation and Bid cleavage. Thus, both ER stress- and mitochondria-mediated death pathways are involved in capsaicin-induced apoptosis.

Fas-associated factor 1 is a negative regulator in capsaicin induced cancer cell apoptosis

Vanilloid receptor1 (VR1/TRPV1) is expressed on peripheral nerves and involved in sensing of temperature and pain. Recent reports have demonstrated that tumor cells express TRPV1 and that capsaicin (CP), a ligand for TRPV1, induces apoptosis in cancer cells. The mechanism underlying CP-induced tumor cell apoptosis remains unclear. Here, we investigated the role of TRPV1 in tumor apoptosis using TRPV1-expressing cancer cell lines. We demonstrate that iodo-resiniferatoxin (I-RTX), an antagonist of TRPV1 does not inhibit CP mediated apoptosis nor is it cytotoxic by itself, but acts as a partial agonist and shows synergistic effect with CP. We further demonstrate that CP treatment degrades Fas-associated factor1 (FAF1); a TRPV1 associated protein. Moreover, using RNA interference with small inhibitory RNAs (siRNA) for FAF1 we observed that down-regulation of FAF1 by siRNA makes the cell susceptible to enhanced apoptosis with CP. In summary, our data shows for the first time that the underlying mechanisms of CP-induced cancer cell apoptosis involves FAF1, a TRPV1 associated protein and serves as an important foundation for further understanding of anticancer activity of CP.