Manjula Vinayak

Anti-carcinogenic action of curcumin by activation of antioxidant defence system and inhibition of NF-κB signalling in lymphoma-bearing mice

NF-κB (nuclear factor κB) plays a significant role in inflammation, immunity, cell proliferation, apoptosis and malignancy. ROS (reactive oxygen species) are among the most important regulating factors of NF-κB. Intracellular ROS are mainly regulated by an endogenous antioxidant defence system. Any disruption of redox balance leads to oxidative stress, which causes a number of pathological conditions including inflammation and malignancy. Increased metabolic activity in cancerous cells leads to oxidative stress, which is further enhanced due to depletion of the endogenous antioxidant defence system. However, the activation and signalling of NF-κB are reported to be inhibited by overexpression and induced activity of antioxidant enzymes. Therefore the present study focuses on the correlation between the endogenous antioxidant defence system, ROS and NF-κB activation during lymphoma growth in mice. The study highlights the anti-carcinogenic role of curcumin by modulation of NF-κB activation and oxidative stress via the endogenous antioxidant defence system. Oxidative stress was monitored by lipid peroxidation, protein carbonylation and antioxidant enzyme activity. NF-κB-mediated signalling was tested by DNA-binding activity. The results reflect that intracellular production of H2O2 in oxidative tumour micro-environment regulates NF-κB activation. Curcumin inhibits oxidative state in the liver of lymphoma-bearing mice by enhancing the transcription and activities of antioxidant enzymes, which in turn modulate activation of NF-κB, leading to a decrease in lymphoma growth. Morphological changes as well as cell proliferation and cell survival assays confirmed reduced lymphoma growth. Thus curcumin contributes to cancer prevention by disrupting the vicious cycle of constant ROS production, responsible for a high oxidative micro-environment for tumour growth.

Anticarcinogenic action of quercetin by downregulation of phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) via induction of p53 in hepatocellular carcinoma (HepG2) cell line

Protein kinase C (PKC) is a key regulator of cell growth and differentiation in mammalian cells and hyperactivation of PKC is believed to play an important role in tumor progression. PKC is downstream to signaling protein of phosphatidylinositol 3-Kinase (PI3K), a known up-regulator of cell proliferation and survival. Accumulation of reactive oxygen species (ROS) triggers oxidative stress in the tumor microenvironment, leading to the hyperactivation of various oxidative stress-stimulated signaling molecules. Quercetin (QUE) is a naturally occurring dietary flavonoid having antioxidant properties. QUE is reported to show antitumor activity both in vitro and in vivo; however, the molecular mechanism is yet to be thoroughly explored. HepG2 cells display cellular functions similar to the normal hepatocytes with high degree of morphological and functional differentiation, therefore HepG2 cell line is chosen as the suitable model for drug targeting. Present study is aimed to establish the signaling pathway involved in the anticarcinogenic action of QUE in HepG2 cell line. HepG2 cells were treated with different doses of QUE. Protein level and gene expression were analysed by Western blotting and RT-PCR, respectively. PKC activity was measured by non-radioactive-tagged phosphorylation. Results showed downregulation of expression of PI3K, PKC, COX-2 and ROS caused by QUE. Additionally, QUE enhanced the expression of p53 and BAX in HepG2 cells. Overall, results of the current study suggested that QUE elicited anticarcinogenic action by upregulation of p53 and BAX in HepG2 cells via downregulation of ROS, PKC, PI3K and COX-2, confirming our earlier report on the animal model.

Long term effect of curcumin in restoration of tumour suppressor p53 and phase-II antioxidant enzymes via activation of Nrf2 signalling and modulation of inflammation in prevention of cancer

Inhibition of carcinogenesis may be a consequence of attenuation of oxidative stress via activation of antioxidant defence system, restoration and stabilization of tumour suppressor proteins along with modulation of inflammatory mediators. Previously we have delineated significant role of curcumin during its long term effect in regulation of glycolytic pathway and angiogenesis, which in turn results in prevention of cancer via modulation of stress activated genes. Present study was designed to investigate long term effect of curcumin in regulation of Nrf2 mediated phase-II antioxidant enzymes, tumour suppressor p53 and inflammation under oxidative tumour microenvironment in liver of T-cell lymphoma bearing mice. Inhibition of Nrf2 signalling observed during lymphoma progression, resulted in down regulation of phase II antioxidant enzymes, p53 as well as activation of inflammatory signals. Curcumin potentiated significant increase in Nrf2 activation. It restored activity of phase-II antioxidant enzymes like GST, GR, NQO1, and tumour suppressor p53 level. In addition, curcumin modulated inflammation via upregulation of TGF-β and reciprocal regulation of iNOS and COX2. The study suggests that during long term effect, curcumin leads to prevention of cancer by inducing phase-II antioxidant enzymes via activation of Nrf2 signalling, restoration of tumour suppressor p53 and modulation of inflammatory mediators like iNOS and COX2 in liver of lymphoma bearing mice.

Queuine promotes antioxidant defence system by activating cellular antioxidant enzyme activities in cancer

Constant generation of Reactive oxygen species (ROS) during normal cellular metabolism of an organism is generally balanced by similar rate of consumption by antioxidants. Imbalance between ROS production and antioxidant defense results in increased level of ROS causing oxidative stress which leads to promotion of malignancy. Queuine is a hyper modified base analogue of guanine, found at first anti-codon position of Q- family of tRNAs. These tRNAs are completely modified with respect to queuosine in terminally differentiated somatic cells, however hypomodification of Q-tRNAs is close association with cell proliferation. Q-tRNA modification is essential for normal development, differentiation and cellular functions. Queuine is a nutrient factor to eukaryotes. It is found to promote cellular antioxidant defense system and inhibit tumorigenesis. The activities of antioxidant enzymes like catalase, SOD, glutathione peroxidase and glutathione reductase are found to be low in Daltons lymphoma ascites transplanted (DLAT) mouse liver compared to normal. However, exogenous administration of queuine to DLAT mouse improves the activities of antioxidant enzymes. The results suggest that queuine promotes antioxidant defense system by increasing antioxidant enzyme activities and in turn inhibits oxidative stress and tumorigenesis.

Modulation of Lactate Dehydrogenase Isozymes by Modified Base Queuine

The modified base queuine is a nutrient factor for lower and higher eukaryotes except yeast. It is synthesized in eubacteria and inserted into the wobble position of specific tRNAs (tRNAGUN) in exchange of guanine at position 34. The tRNAs of Q family are completely modified in terminally differentiated somatic cells. However, mainly free queuine is present in embryonic and fast proliferating cells, tRNA remains Q deficient. Lactate dehydrogenase (LDH) A mRNA and LDH A protein is known to increase when cells are grown in hypoxic conditions. In the present study, the level of LDH isozymes is analyzed in different tissues of normal and cancerous (DLA) mice and the effect of queuine treatment on LDH isozyme is observed. LDH A isozyme is shown to increase in serum and liver of DLA mice. The level and activity of LDH A decreases on queuine treatment. In skeletal muscle and heart, LDH A isozyme decreases while LDH B increases in DLA mice. Queuine administration leads to change back towards normal. In case of brain, LDH A increases but LDH B decreases in DLA mice. Queuine treatment leads to decrease in A4 anaerobic isozymes of LDH. The results suggest that queuine suppresses anaerobic glycolytic pathway, which leads to tumor suppression of DLA mice.

Effect of Terminalia arjuna on antioxidant defense system in cancer

Constant production of reactive oxygen species (ROS) during aerobic metabolism is balanced by antioxidant defense system of an organism. Although low level of ROS is important for various physiological functions, its accumulation has been implicated in the pathogenesis of age-related diseases such as cancer and coronary heart disease and neurodegenerative disorders such as Alzheimer’s disease. It is generally assumed that frequent consumption of phytochemicals derived from vegetables, fruits, tea and herbs may contribute to shift the balance towards an adequate antioxidant status. The present study is aimed to investigate the effect of aqueous extract of medicinal plant Terminalia arjuna on antioxidant defense system in lymphoma bearing AKR mice. Antioxidant action of T. arjuna is monitored by the activities of catalase, superoxide dismutase and glutathione S transferase which constitute major antioxidant defense system by scavenging ROS. These enzyme activities are low in lymphoma bearing mice indicating impaired antioxidant defense system. Oral administration of different doses of aqueous extract of T. arjuna causes significant elevation in the activities of catalase, superoxide dismutase and glutathione S transferase. T. arjuna is found to down regulate anaerobic metabolism by inhibiting the activity of lactate dehydrogenase in lymphoma bearing mice, which was elevated in untreated cancerous mice. The results indicate the antioxidant action of aqueous extract of T. arjuna, which may play a role in the anti carcinogenic activity by reducing the oxidative stress along with inhibition of anaerobic metabolism.

Quercetin Regresses Dalton's Lymphoma Growth via Suppression of PI3K/AKT Signaling Leading to Upregulation of p53 and Decrease in Energy Metabolism

Various oncogenes are associated with deregulation in cell proliferation, apoptosis, and cell survival, which ultimately cause cancerous growth. Phosphatidylinositol 3-kinase (PI3K) mediated signaling plays a key role in malignant transformation. Cell proliferation and cell survival of tumor cell are induced by hyper activation of PI3K, AKT1, glycolytic enzyme LDH-A, and inactivation of tumor suppressor gene p53. Dietary flavonoids such as quercetin are considered a powerful modulator of different cellular signaling pathways. The present study is focused on the role of quercetin on regulation of PI3K/AKT pathways in Daltons lymphoma mice. Effect of quercetin was analyzed in ascite cells in terms of cell viability, glycolytic metabolism as well as expression, and level of PI3K (regulatory and catalytic subunit), AKT1, and p53 using standard methods. Results reflect hyperactivation of PI3K signaling in ascite cells of Daltons lymphoma mice, leading to activation of AKT1 and inactivation of p53. Quercetin modulates the pathway toward suppression of lymphoma. Glycolytic metabolism was also downregulated by quercetin. Its tumor suppressor activity was confirmed by morphological parameters and longevity of mice. The findings suggest that quercetin may contribute to lymphoma prevention by downregulating PI3K–AKT1–p53 pathway as well as by glycolytic metabolism.

Long Term Effect of Curcumin in Regulation of Glycolytic Pathway and Angiogenesis via Modulation of Stress Activated Genes in Prevention of Cancer

Oxidative stress, an important factor in modulation of glycolytic pathway and induction of stress activated genes, is further augmented due to reduced antioxidant defense system, which promotes cancer progression via inducing angiogenesis. Curcumin, a naturally occurring chemopreventive phytochemical, is reported to inhibit carcinogenesis in various experimental animal models. However, the underlying mechanism involved in anticarcinogenic action of curcumin due to its long term effect is still to be reported because of its rapid metabolism, although metabolites are accumulated in tissues and remain for a longer time. Therefore, the long term effect of curcumin needs thorough investigation. The present study aimed to analyze the anticarcinogenic action of curcumin in liver, even after withdrawal of treatment in Daltons lymphoma bearing mice. Oxidative stress observed during lymphoma progression reduced antioxidant enzyme activities, and induced angiogenesis as well as activation of early stress activated genes and glycolytic pathway. Curcumin treatment resulted in activation of antioxidant enzyme super oxide dismutase and down regulation of ROS level as well as activity of ROS producing enzyme NADPH:oxidase, expression of stress activated genes HIF-1α, cMyc and LDH activity towards normal level. Further, it lead to significant inhibition of angiogenesis, observed via MMPs activity, PKCα and VEGF level, as well as by matrigel plug assay. Thus findings of this study conclude that the long term effect of curcumin shows anticarcinogenic potential via induction of antioxidant defense system and inhibition of angiogenesis via down regulation of stress activated genes and glycolytic pathway in liver of lymphoma bearing mice.

Anti-carcinogenic action of ellagic acid mediated via modulation of oxidative stress regulated genes in Dalton lymphoma bearing mice.

Abstract An elevated level of reactive oxygen species (ROS) in a cancerous condition causes oxidative stress which in turn activates a number of genes, and therefore an interruption in the oxidative microenvironment should be able to inactivate these genes, contributing to cancer prevention. The present work was designed to evaluate the role of ellagic acid in the modulation of protein kinase Cα (PKCα) activity and expression and its correlation with the oncogene, c-Myc, and tumor suppressor gene, transforming growth factor-β (TGF-β1), in lymphoma bearing mice. We also evaluated its implication for cell viability. Our results show that ellagic acid leads to down-regulation of the expression and activity of PKCα via decreasing the oxidative stress, measured in terms of lipid peroxidation and protein carbonylation. It also reduces c-Myc expression and improves TGF-β1 expression besides decreasing cell viability in Dalton lymphoma bearing mice, which supports its anti-carcinogenic action.

Modulation of PKC signaling and induction of apoptosis through suppression of reactive oxygen species and tumor necrosis factor receptor 1 (TNFR1): key role of quercetin in cancer prevention

Cancer cells are characterized by increased production of reactive oxygen species (ROS) and an altered redox environment as compared to normal cells. Continuous accumulation of ROS triggers oxidative stress leading to hyper-activation of signaling pathways that promote cell proliferation, survival, and metabolic adaptation to the tumor microenvironment. Therefore, antioxidants are proposed to contribute to cancer prevention. Protein kinase C (PKC) is a crucial regulator of diverse cellular processes and contributes to cancer progression. The activation of PKC is partially dependent on ROS signaling. In the present study, cancer preventive activity of natural flavonoid quercetin is analyzed in ascite cells of Dalton’s lymphoma-bearing mice. The total ROS level and activity of PKC were downregulated after quercetin treatment in lymphoma-bearing mice. Quercetin modulates the expression of almost all isozymes of classical, novel, and atypical PKC as well as downregulates the level and expression of PKCα. Further, quercetin improves apoptotic potential, as observed by the levels of caspase 3, caspase 9, PARP, PKCδ, and nuclear condensation. Additionally, quercetin reduces cell survival and promotes death receptor-mediated apoptosis via differential localization of the TNFR1 level in ascite cells. The overall result suggests the cancer preventive activity of quercetin via the induction of apoptosis and modulates PKC signaling with the reduction of oxidative stress in ascite cells of lymphoma-bearing mice.