Srabanti Rakshit

Involvement of ROS in chlorogenic acid-induced apoptosis of Bcr-Abl+ CML cells

Chlorogenic acid (Chl) has been reported to possess a wide range of biological and pharmacological properties including induction of apoptosis of Bcr-Abl(+) chronic myeloid leukemia (CML) cell lines and clinical leukemia samples via inhibition of Bcr-Abl phosphorylation. Here we studied the mechanisms of action of Chl in greater detail. Chl treatment induced an early accumulation of intracellular reactive oxygen species (ROS) in Bcr-Abl(+) cells leading to downregulation of Bcr-Abl phosphorylation and apoptosis. Chl treatment upregulated death receptor DR5 and induced loss of mitochondrial membrane potential accompanied by release of cytochrome c from the mitochondria to the cytosol. Pharmacological inhibition of caspase-8 partially inhibited apoptosis, whereas caspase-9 and pan-caspase inhibitor almost completely blocked the killing. Knocking down DR5 using siRNA completely attenuated Chl-induced caspase-8 cleavage but partially inhibited apoptosis. Antioxidant NAC attenuated Chl-induced oxidative stress-mediated inhibition of Bcr-Abl phosphorylation, DR5 upregulation, caspase activation and CML cell death. Our data suggested the involvement of parallel death pathways that converged in mitochondria. The role of ROS in Chl-induced death was confirmed with primary leukemia cells from CML patients in vitro as well as in vivo in nude mice bearing K562 xenografts. Collectively, our results establish the role of ROS for Chl-mediated preferential killing of Bcr-Abl(+) cells.

Immunotherapeutic efficacy of Mycobacterium indicus pranii in eliciting anti-tumor T cell responses: Critical roles of IFNγ

Mycobacterium indicus pranii (MIP) is approved for use as an adjuvant (Immuvac/Cadi‐05) in the treatment of leprosy. In addition, its efficacy is being investigated in clinical trials on patients with tuberculosis and different tumors. To evaluate and delineate the mechanisms by which autoclaved MIP enhances anti‐tumor responses, the growth of solid tumors consisting of Sp2/0 (myeloma) and EL4 (thymoma) cells was studied in BALB/c and C57BL/6 mice, respectively. Treatment of mice with a single intra‐dermal (i.d.) injection of MIP 3 days after Sp2/0 implantation greatly suppresses tumor growth. MIP treatment of tumor bearing mice lowers Interleukin (IL)6 but increases IL12p70 and IFNγ amounts in sera. Also, increase in CD8+ T cell mediated lysis of specific tumor targets and production of high amounts of IL2 and IFNγ by CD4+ T cells upon stimulation with specific tumor antigens in MIP treated mice is observed. Furthermore, MIP is also effective in reducing the growth of EL4 tumors; however, this efficacy is reduced in Ifnγ−/− mice. In fact, several MIP mediated anti‐tumor responses are greatly abrogated in Ifnγ−/− mice: increase in serum Interleukin (IL)12p70 amounts, induction of IL2 and lysis of EL4 targets by splenocytes upon stimulation with specific tumor antigens. Interestingly, tumor‐induced increase in serum IL12p70 and IFNγ and reduction in growth of Sp2/0 and EL4 tumors by MIP are not observed in nonobese diabetic severe combined immunodeficiency mice. Overall, our study clearly demonstrates the importance of a functional immune network, in particular endogenous CD4+ and CD8+ T cells and IFNγ, in mediating the anti‐tumor responses by MIP.

N-acetyl cysteine enhances imatinib-induced apoptosis of Bcr-Abl+ cells by endothelial nitric oxide synthase-mediated production of nitric oxide

IntroductionImatinib, a small-molecule inhibitor of the Bcr-Abl kinase, is a successful drug for treating chronic myeloid leukemia (CML). Bcr-Abl kinase stimulates the production of H2O2, which in turn activates Abl kinase. We therefore evaluated whether N-acetyl cysteine (NAC), a ROS scavenger improves imatinib efficacy.Materials and methodsEffects of imatinib and NAC either alone or in combination were assessed on Bcr-Abl+ cells to measure apoptosis. Role of nitric oxide (NO) in NAC-induced enhanced cytotoxicity was assessed using pharmacological inhibitors and siRNAs of nitric oxide synthase isoforms. We report that imatinib-induced apoptosis of imatinib-resistant and imatinib-sensitive Bcr-Abl+ CML cell lines and primary cells from CML patients is significantly enhanced by co-treatment with NAC compared to imatinib treatment alone. In contrast, another ROS scavenger glutathione reversed imatinib-mediated killing. NAC-mediated enhanced killing correlated with cleavage of caspases, PARP and up-regulation and down regulation of pro- and anti-apoptotic family of proteins, respectively. Co-treatment with NAC leads to enhanced production of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS). Involvement of eNOS dependent NO in NAC-mediated enhancement of imatinib-induced cell death was confirmed by nitric oxide synthase (NOS) specific pharmacological inhibitors and siRNAs. Indeed, NO donor sodium nitroprusside (SNP) also enhanced imatinib-mediated apoptosis of Bcr-Abl+ cells.ConclusionNAC enhances imatinib-induced apoptosis of Bcr-Abl+ cells by endothelial nitric oxide synthase-mediated production of nitric oxide.

Identification of Early Biomarkers during Acetaminophen-Induced Hepatotoxicity by Fourier Transform Infrared Microspectroscopy

Acetaminophen is a widely prescribed drug used to relieve pain and fever; however, it is a leading cause of drug-induced liver injury and a burden on public healthcare. In this study, hepatotoxicity in mice post oral dosing of acetaminophen was investigated using liver and sera samples with Fourier Transform Infrared microspectroscopy. The infrared spectra of acetaminophen treated livers in BALB/c mice show decrease in glycogen, increase in amounts of cholesteryl esters and DNA respectively. Rescue experiments using L-methionine demonstrate that depletion in glycogen and increase in DNA are abrogated with pre-treatment, but not post-treatment, with L-methionine. This indicates that changes in glycogen and DNA are more sensitive to the rapid depletion of glutathione. Importantly, analysis of sera identified lowering of glycogen and increase in DNA and chlolesteryl esters earlier than increase in alanine aminotransferase, which is routinely used to diagnose liver damage. In addition, these changes are also observed in C57BL/6 and Nos2 −/− mice. There is no difference in the kinetics of expression of these three molecules in both strains of mice, the extent of damage is similar and corroborated with ALT and histological analysis. Quantification of cytokines in sera showed increase upon APAP treatment. Although the levels of Tnfα and Ifnγ in sera are not significantly affected, Nos2 −/− mice display lower Il6 but higher Il10 levels during this acute model of hepatotoxicity. Overall, this study reinforces the growing potential of Fourier Transform Infrared microspectroscopy as a fast, highly sensitive and label-free technique for non-invasive diagnosis of liver damage. The combination of Fourier Transform Infrared microspectroscopy and cytokine analysis is a powerful tool to identify multiple biomarkers, understand differential host responses and evaluate therapeutic regimens during liver damage and, possibly, other diseases.

Interferon-gamma induced cell death: Regulation and contributions of nitric oxide, cJun N-terminal kinase, reactive oxygen species and peroxynitrite

Interferon-gamma (Ifnγ), a known immunomodulatory cytokine, regulates cell proliferation and survival. In this study, the mechanisms leading to the selective susceptibility of some tumor cells to Ifnγ were deciphered. Seven different mouse tumor cell lines tested demonstrated upregulation of MHC class I to variable extents with Ifnγ; however, only the cell lines, H6 hepatoma and L929 fibrosarcoma, that produce higher amounts of nitric oxide (NO) and reactive oxygen species (ROS) are sensitive to Ifnγ-induced cell death. NO inhibitors greatly reduce Ifnγ-induced ROS; however, ROS inhibitors did not affect the levels of Ifnγ-induced NO, demonstrating that NO regulates ROS. Consequently, NO inhibitors are more effective, compared to ROS inhibitors, in reducing Ifnγ-induced cell death. Further analysis revealed that Ifnγ induces peroxynitrite and 3-nitrotyrosine amounts and a peroxynitrite scavenger, FeTPPS, reduces cell death. Ifnγ treatment induces the phosphorylation of c-jun N-terminal kinase (Jnk) in H6 and L929 but not CT26, a colon carcinoma cell line, which is resistant to Ifnγ-mediated death. Jnk activation downstream to NO leads to induction of ROS, peroxynitrite and cell death in response to Ifnγ. Importantly, three cell lines tested, i.e. CT26, EL4 and Neuro2a, that are resistant to cell death with Ifnγ alone become sensitive to the combination of Ifnγ and NO donor or ROS inducer in a peroxynitrite-dependent manner. Overall, this study delineates the key roles of NO as the initiator and Jnk, ROS, and peroxynitrite as the effectors during Ifnγ-mediated cell death. The implications of these findings in the Ifnγ-mediated treatment of malignancies are discussed.

UDP-glucose 4, 6-dehydratase activity plays an important role in maintaining cell wall integrity and virulence of Candida albicans.

Candida albicans, a human fungal pathogen, undergoes morphogenetic changes that are associated with virulence. We report here that GAL102 in C. albicans encodes a homolog of dTDP-glucose 4,6-dehydratase, an enzyme that affects cell wall properties as well as virulence of many pathogenic bacteria. We found that GAL102 deletion leads to greater sensitivity to antifungal drugs and cell wall destabilizing agents like Calcofluor white and Congo red. The mutant also formed biofilms consisting mainly of hyphal cells that show less turgor. The NMR analysis of cell wall mannans of gal102 deletion strain revealed that a major constituent of mannan is missing and the phosphomannan component known to affect virulence is greatly reduced. We also observed that there was a substantial reduction in the expression of genes involved in biofilm formation but increase in the expression of genes encoding glycosylphosphatidylinositol-anchored proteins in the mutant. These, along with altered mannosylation of cell wall proteins together might be responsible for multiple phenotypes displayed by the mutant. Finally, the mutant was unable to grow in the presence of resident peritoneal macrophages and elicited a weak pro-inflammatory cytokine response in vitro. Similarly, this mutant elicited a poor serum pro-inflammatory cytokine response as judged by IFNγ and TNFα levels and showed reduced virulence in a mouse model of systemic candidiasis. Importantly, an Ala substitution for a conserved Lys residue in the active site motif YXXXK, that abrogates the enzyme activity also showed reduced virulence and increased filamentation similar to the gal102 deletion strain. Since inactivating the enzyme encoded by GAL102 makes the cells sensitive to antifungal drugs and reduces its virulence, it can serve as a potential drug target in combination therapies for C. albicans and related pathogens.

Circulating Mycobacterium tuberculosis DosR latency antigen-specific, polyfunctional, regulatory IL10+ Th17 CD4 T-cells differentiate latent from active tuberculosis

The functional heterogeneity of T cell responses to diverse antigens expressed at different stages of Mycobacterium tuberculosis (Mtb) infection, in particular early secreted versus dormancy related latency antigens expressed later, that distinguish subjects with latent (LTBI), pulmonary (PTB) or extrapulmonary (EPTB) tuberculosis remains unclear. Here we show blood central memory CD4 T-cell responses specific to Mtb dormancy related (DosR) latency, but not classical immunodominant secretory antigens, to clearly differentiate LTBI from EPTB and PTB. The polyfunctionality score integrating up to 31 DosR-specific CD4 T-cell functional profiles was significantly higher in LTBI than EPTB or PTB subjects. Further analysis of 256 DosR-specific T-cell functional profiles identified regulatory IL10 + Th17 cells (IL10+IL17A+IL17F+IL22+) to be significantly enriched in LTBI; in contrast to pro-inflammatory Th17 cells (IFNγ+IL17A+/IL10−) in the blood and lung of EPTB and PTB subjects respectively. A blood polyfunctional, Mtb DosR latency antigen specific, regulatory, central memory response is therefore a novel functional component of T-cell immunity in latent TB and potential correlate of protection.

Infrared spectroscopic studies to understand the effect of drugs at molecular level

In the recent past, there have been enormous efforts to understand effect of drugs on human body. Prior to understand the effect of drugs on human body most of the experiments are carried out on cells or model organisms. Here we present our study on the effect of chemotherapeutic drugs on cancer cells and the acetaminophen (APAP) induced hepatotoxicity in mouse model. Histone deacetylase inhibitors (HDIs) have attracted attention as potential drug molecules for the treatment of cancer. These are the chemotherapeutic drugs which have indirect mechanistic action against cancer cells via acting against histone deacetylases (HDAC). It has been known that different HDAC enzymes are over-expressed in various types of cancers for example; HDAC1 is over expressed in prostate, gastric and breast carcinomas. Therefore, in order to optimise chemotherapy, it is important to determine the efficacy of various classes of HDAC inhibitor drugs against variety of over-expressed HDAC enzymes. In the present study, FTIR microspectroscopy has been employed to predict the acetylation and propionylation brought in by HDIs. The liver plays an important role in cellular metabolism and is highly susceptible to drug toxicity. APAP which is an analgesic and antipyretic drug is extensively used for therapeutic purposes and has become the most common cause of acute liver failure (ALF). In the current study, we have focused to understand APAP induced hepatotoxicity using FTIR microspectroscopy. In the IR spectrum the bands corresponding to glycogen, ester group and were found to be suitable markers to predict liver injury at early time point (0.5hr) due to APAP both in tissue and serum in comparison to standard biochemical assays. Our studies show the potential of FTIR spectroscopy as a rapid, sensitive and non invasive detection technique for future clinical diagnosis.