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Reactive oxygen species are important regulators of protozoal infection. Promastigotes of Leishmania donovani, the causative agent of Kala-azar, undergo an apoptosis-like death upon exposure to H 2 O 2 . The present study shows that upon activation of death response by H 2 O 2 , a dose-and time-dependent loss of mitochondrial membrane potential occurs. This loss is accompanied by a depletion of cellular glutathione, but cardiolipin content or thiol oxidation status remains unchanged. ATP levels are reduced within the first 60 min of exposure as a result of mitochondrial membrane potential loss. A tight link exists between changes in cytosolic Ca 2؉ homeostasis and collapse of the mitochondrial membrane potential, but the dissipation of the potential is independent of elevation of cytosolic Na ؉ and mitochondrial Ca 2؉ . Partial inhibition of cytosolic Ca 2؉ increase achieved by chelating extracellular or intracellular Ca 2؉ by the use of appropriate agents resulted in significant rescue of the fall of the mitochondrial membrane potential and apoptosis-like death. It is further demonstrated that the increase in cytosolic Ca 2؉ is an additive result of release of Ca 2؉ from intracellular stores as well as by influx of extracellular Ca 2؉ through flufenamic acid-sensitive non-selective cation channels; contribution of the latter was larger. Mitochondrial changes do not involve opening of the mitochondrial transition pore as cyclosporin A is unable to prevent mitochondrial membrane potential loss. An antioxidant like Nacetylcysteine is able to inhibit the fall of the mitochondrial membrane potential and prevent apoptosis-like death. Together, these findings show the importance of non-selective cation channels in regulating the response of L. donovani promastigotes to oxidative stress that triggers downstream signaling cascades leading to apoptosis-like death.Mitochondria are pivotal in controlling cell life and death (1). Maintenance of proper mitochondrial transmembrane potential (⌬ m ) 1 is essential for the survival of the cell as it drives the synthesis of ATP and maintains oxidative phosphorylation (2). Recently, the study of mitochondrial potential has become a focus of apoptosis regulation as many investigations demonstrate a major functional impact of mitochondrial alterations on apoptosis (2). Apoptosis is a process of cell death in which the cells undergo nuclear and cytoplasmic shrinkage; the chromatin is condensed and partitioned into multiple fragments, and finally the cells are broken into multiple membrane-bound bodies. In a number of experimental systems, disruption of ⌬ m constitutes a constant early event of the apoptotic process that precedes nuclear disintegration (3-5). For example, in thymocytes or tumor necrosis factor-stimulated U937 cells (3, 6), thymocytes or imexon-treated myeloma cells (5, 7), and PC-12 cells (8), a loss of ⌬ m occur as an early change associated with apoptosis. Lymphocytes with low ⌬ m show irreversible commitment to apoptosis in comparison to cells with high ⌬ m that do...

The capability of the obligate intracellular parasites like Leishmania donovani to survive within the host cell parasitophorous vacuoles as nonmotile amastigotes determines disease pathogenesis, but the mechanism of elimination of the parasites from these vacuoles are not well understood. By using the anti-leishmanial drug potassium antimony tartrate, we demonstrate that, upon drug exposure, intracellular L. donovani amastigotes undergo apoptotic death characterized by nuclear DNA fragmentation and externalization of phosphatidylserine. Changes upstream of DNA fragmentation included generation of reactive oxygen species like superoxide, nitric oxide, and hydrogen peroxide that were primarily concentrated in the parasitophorous vacuoles. In the presence of antioxidants like N-acetylcysteine or Mn(III) tetrakis(4-benzoic acid)porphyrin chloride, an inhibitor of inducible nitric-oxide synthase, a diminution of reactive oxygen species generation and improvement of amastigote survival were observed, suggesting a close link between drug-induced oxidative stress and amastigote death. Changes downstream to reactive oxygen species increase involved elevation of intracellular Ca 2؉ concentrations in both the parasite and the host that was preventable by antioxidants. Flufenamic acid, a non-selective cation channel blocker, decreased the elevation of Ca 2؉ in both the cell types and reduced amastigote death, thus establishing a central role of Ca 2؉ in intracellular parasite clearance. This influx of Ca 2؉ was preceded by a fall in the amastigote mitochondrial membrane potential. Therefore, this study projects the importance of flufenamic acid-sensitive non-selective cation channels as important modulators of antimonial efficacy and lends credence to the suggestion that, within the host cell, apoptosis is the preferred mode of death for the parasites.

Dietary polyphenols have been found to possess preventive and therapeutic potential against several types of cancers. We investigated the effect of ellagic acid on colon cancer induced by 1,2-dimethylhydrazine in rats. Male Wistar albino rats were divided into four groups. Group 1 served as control, group 2 rats received ellagic acid 60 mg ⁄ kg bodyweight ⁄ every day p.o. throughout the experiment. Rats from groups 3 and 4 were given subcutaneous (s.c.) injections of 1,2-dimethylhydrazine (20 mg ⁄ kg body weight) once a week for the first 15 weeks; rats in group 4 received ellagic acid as in group 2 after the last injection of 1,2-dimethylhydrazine and continued till the end of the experimental period of 30 weeks. 1,2-dimethylhydrazine-induced rats exhibited alterations in cancer tumour markers [5¢-nucleotidase (5¢-ND), gamma glutamyl transpeptidase (c-GT), carcinoembryonic antigen (CEA), alphafetoprotein (AFP) and cathepsin-D (CD)]; pathophysiological markers [alkaline phosphatase (ALP) and lactate dehydrogenase (LDH)] and oral administration of ellagic acid restored the levels of these marker enzymes. Nuclear factor-kappa B (NF-jB) actively involved in the regulation of both pro-inflammatory proteins [inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2)] and pro-inflammatory cytokines [tumour necrosis factor (TNF)-a and interleukin (IL)-6] and in our study 1,2-dimethylhydrazine-induced group exhibited elevated expressions of all these inflammatory proteins. Ellagic acid administration reduced the expressions of NF-jB, COX-2, iNOS, TNF-a and IL-6 as confirmed by immunohistochemical, immunoblot and immunofluorescence analysis during 1,2-dimethylhydrazineinduced colon carcinogenesis. In conclusion, ellagic acid demonstrates anti-inflammatory property by iNOS, COX-2, TNF-a and IL-6 down-regulation due to inhibition of NF-jB and exerts its chemopreventive effect on colon carcinogenesis.Colorectal cancer is one of the leading causes of tumourrelated deaths and despite its high prevalence, the underlying pathological mechanisms remain elusive [1]. The incidence in Asia was estimated to rank 3rd in both genders for all malignant diseases in 2008 [2]. Colorectal cancer is a multistep process affected by environmental and genetic factors, which leads to normal colonic epithelium to dysplasia followed by a benign precursor stage, the pre-malignant polyp and can progress to invasive disease. Besides a genetic pre-disposition, diet also determines the risk for colon cancer and predominantly diets rich in fruits and vegetables diminish the risk of the disease [3]. 1,2-Dimethylhydrazine-induced model is utilized frequently, as it is similar to histopathological and molecular characteristics of human colon cancer model [4]. 1,2-Dimethylhydrazine is metabolized in liver to form azoxymethane and methylazoxymethanol later on transported to colon via bile or blood to generate its ultimate carcinogenic metabolite, diazonium ion which elicits an oxidative stress by methylating biomolecules of colonic epithe...

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