Oligonucleosomal Fragmentation Research Articles

Microhomology-mediated circular DNA formation from oligonucleosomal fragments during spermatogenesis.

The landscape of extrachromosomal circular DNA (eccDNA) during mammalian spermatogenesis, as well as the biogenesis mechanism, remains to be explored. Here, we revealed widespread eccDNA formation in human sperms and mouse spermatogenesis. We noted that germline eccDNAs are derived from oligonucleosomal DNA fragmentation in cells likely undergoing cell death, providing a potential new way for quality assessment of human sperms. Interestingly, small-sized eccDNAs are associated with euchromatin, while large-sized ones are preferentially generated from heterochromatin. By comparing sperm eccDNAs with meiotic recombination hotspots and structural variations, we found that they are barely associated with de novo germline deletions. We further developed a bioinformatics pipeline to achieve nucleotide-resolution eccDNA detection even with the presence of microhomologous sequences that interfere with precise breakpoint identification. Empowered by our method, we provided strong evidence to show that microhomology-mediated end joining is the major eccDNA biogenesis mechanism. Together, our results shed light on eccDNA biogenesis mechanism in mammalian germline cells.

Microhomology-mediated circular DNA formation from oligonucleosomal fragments during spermatogenesis

The landscape of extrachromosomal circular DNA (eccDNA) during mammalian spermatogenesis, as well as the biogenesis mechanism, remains to be explored. Here, we revealed widespread eccDNA formation in human sperms and mouse spermatogenesis. We noted that germline eccDNAs are derived from oligonucleosomal DNA fragmentation in cells likely undergoing cell death, providing a potential new way for quality assessment of human sperms. Interestingly, small-sized eccDNAs are associated with euchromatin, while large-sized ones are preferentially generated from heterochromatin. By comparing sperm eccDNAs with meiotic recombination hotspots and structural variations, we found that they are barely associated with de novo germline deletions. We further developed a bioinformatics pipeline to achieve nucleotide-resolution eccDNA detection even with the presence of microhomologous sequences that interfere with precise breakpoint identification. Empowered by our method, we provided strong evidence to show that microhomology-mediated end joining is the major eccDNA biogenesis mechanism. Together, our results shed light on eccDNA biogenesis mechanism in mammalian germline cells.

Contribution of Myocyte Apoptosis to Myocardial Injury in an <i>in Vivo</i> Rabbit Preparation of Ischemia-Reperfusion

Objective: Exposure of the heart to repeated, brief episodes of coronary occlusion/reperfusion prevents lethal myocyte injury. Necrosis and apoptosis, two seemingly distinct mechanisms of cell death caused by ischemia could contribute independently to progressive loss of myocardium. Studies suggest that ischemic conditioning (IC) lessens myocyte injury by decreasing apoptosis. The goal of this study was to examine cell death in rabbit hearts subject to ischemia-reperfusion injury without (nIC) or with pretreatment by IC. Methods: In the control study, anesthetized, male rabbits (n = 4/group) underwent 30-min regional coronary occlusion (CO) and either 3, 6 or 24h reperfusion (REP). In the IC study, rabbits were pretreated by IC (2 cycles of 5-min CO and 10-min REP) before 30-min CO and subsequent REP. Additional groups were evaluated with 60, or 120-min CO followed by up to 96 h REP. Agarose electrophoresis was used to detect DNA laddering and poly (ADP-ribose) polymerase (PARP; chromatin bound nuclear DNA repair enzyme) was assessed in myocardial biopsies. Results: Genomic DNA from nIC and IC hearts showed no oligonucleosomal fragmentation. In addition, we did not detect any cleavage of PARP; however, myocardial PARP levels decreased when CO and REP durations were prolonged. Conclusion:Absence of genomic DNA fragmentation or PARP cleavage in an in vivo preparation of ischemia-reperfusion injury does not support the view that apoptosis contributes markedly to post-ischemic tissue necrosis.

In vitro Evaluation of Programmed Cell Death in the Immune System of Pacific Oyster Crassostrea gigas by the Effect of Marine Toxins.

Programmed cell death (PCD) is an essential process for the immune system's development and homeostasis, enabling the remotion of infected or unnecessary cells. There are several PCD's types, depending on the molecular mechanisms, such as non-inflammatory or pro-inflammatory. Hemocytes are the main component of cellular immunity in bivalve mollusks. Numerous infectious microorganisms produce toxins that impair hemocytes functions, but there is little knowledge on the role of PCD in these cells. This study aims to evaluate in vitro whether marine toxins induce a particular type of PCD in hemocytes of the bivalve mollusk Crassostrea gigas during 4 h at 25°C. Hemocytes were incubated with two types of marine toxins: non-proteinaceous toxins from microalgae (saxitoxin, STX; gonyautoxins 2 and 3, GTX2/3; okadaic acid/dynophysistoxin-1, OA/DTX-1; brevetoxins 2 and 3, PbTx-2,-3; brevetoxin 2, PbTx-2), and proteinaceous extracts from bacteria (Vibrio parahaemolyticus, Vp; V. campbellii, Vc). Also, we used the apoptosis inducers, staurosporine (STP), and camptothecin (CPT). STP, CPT, STX, and GTX 2/3, provoked high hemocyte mortality characterized by apoptosis hallmarks such as phosphatidylserine translocation into the outer leaflet of the cell membrane, exacerbated chromatin condensation, DNA oligonucleosomal fragments, and variation in gene expression levels of apoptotic caspases 2, 3, 7, and 8. The mixture of PbTx-2,-3 also showed many apoptosis features; however, they did not show apoptotic DNA oligonucleosomal fragments. Likewise, PbTx-2, OA/DTX-1, and proteinaceous extracts from bacteria Vp, and Vc, induced a minor degree of cell death with high gene expression of the pro-inflammatory initiator caspase-1, which could indicate a process of pyroptosis-like PCD. Hemocytes could carry out both PCD types simultaneously. Therefore, marine toxins trigger PCD's signaling pathways in C. gigas hemocytes, depending on the toxin's nature, which appears to be highly conserved both structurally and functionally.

The role of the DFF40/CAD endonuclease in genomic stability.

Maintenance of genomic stability in cells is primordial for cellular integrity and protection against tumor progression. Many factors such as ultraviolet light, oxidative stress, exposure to chemical reagents, particularly mutagens and radiation, can alter the integrity of the genome. Thus, human cells are equipped with many mechanisms that prevent these irreversible lesions in the genome, as DNA repair pathways, cell cycle checkpoints, and telomeric function. These mechanisms activate cellular apoptosis to maintain DNA stability. Emerging studies have proposed a new protein in the maintenance of genomic stability: the DNA fragmentation factor (DFF). The DFF40 is an endonuclease responsible of the oligonucleosomal fragmentation of the DNA during apoptosis. The lack of DFF in renal carcinoma cells induces apoptosis without oligonucleosomal fragmentation, which poses a threat to genetic information transfer between cancerous and healthy cells. In this review, we expose the link between the DFF and genomic instability as the source of disease development.

Rosmarinic acid inhibits programmed cell death in Solanum tuberosum L. calli under high salinity

Oxidative stress induced by salinity is a prime cause of cell death when Na+ toxicity becomes unbearable. We explored the effect of rosmarinic acid (RA) on the Solanum tuberosum L. cv. Desiree calli against salt-induced programmed cell death (PCD). We showed that PCD events were triggered in calli under 250 mM NaCl by the loss of plasma membrane integrity as measured by the amount of malondialdehyde (MDA) in the cytoplasm, the degree of DNA degradation resulting from the cleavage of nuclear DNA into oligonucleosomal fragments in apoptotic cells, the presence of TUNEL-positive nuclei (90 ± 0.005%) damage in genomic DNA, and activation of caspase 3-like protease. Callus Formation Medium (CFM) supplemented with RA led to the suppression of salt-induced cell death and a dramatic decrease in the MDA level and frequency of TUNEL-positive nuclei under salinity to 4 ± and 7.3 ± % in the presence of 50 and 350 μM RA, respectively. The application of RA also resulted in an increase in GSH content and maintenance of a high GSH/GSSG ratio. Interestingly, these reductions in PCD were accompanied by inhibiting caspase 3-like protease activities due to RA under salinity. Molecular docking predicted high binding energies of RA for binding to subtilisin-like protease (StSCTc-3), which has caspase-3 like activity in Solanum tuberosum, near the active site. This finding supports the notion of a role for RA in PCD protection in plants, which is consistent with earlier reports in animal cells.

Sucrose alleviated programmed cell death in broccoli after harvest

Abstract The effect of sucrose treatment on morphological and biochemical features of programmed cell death (PCD) in broccoli florets was explored. The apoptosis of untreated and treated cells was evaluated by flow cytometry (FCM) and by laser scanning confocal microscopy (LSCM). DNA ladders, resulting from the cleavage of nuclear DNA into oligonucleosomal fragments in PCD, were evaluated by gel electrophoresis. DNA frag-mentation and nuclear DNA condensation were further confirmed by using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end in situ labeling (TUNEL). The results revealed that sucrose treatment inhibited DNA degradation, and delayed the early apoptosis of broccoli cell as demonstrated with FCM and LSCM. DNA laddering was observed in control broccoli florets, which could not be detected in sucrose-treated samples. In addition, the caspase-like activities in broccoli cells were suppressed under sucrose treatment. Taken together, our results suggested that PCD was delayed in sucrose-treated broccoli florets, which provided a new model to investigate the mechanism of sugar in regulating PCD during postharvest storage.

Programmed cell death in soybean seed coats

Seed coat is the tissue which establishes an interface between the seed inner tissues and external environment. Our group has shown that cowpea seed coat undergoes coordinated events of programmed cell death (PCD) during development. In relation to germinating seed coats, little is known on PCD events. The goal here was to investigate the biochemical aspects of germinating soybean seed coat, focusing on proteolytic activities related to PCD. In gel and in solution activity profiles of quiescent and germinating seed coat extracts revealed a complex pattern of caspase- and metacaspase-like cysteine protease activities. Trypsin inhibitor and reserve proteins were revealed as potential substrates for these proteases. A pancaspase inhibitor (z-VAD-CHO) affected the radicle length of seeds germinated under its presence. Ultrastructural analysis showed the absence of cell organelles in all seed coat layers after imbibition, while oligonucleosome fragments peaked at 72 h after imbibition (HAI). Altogether, the data suggest the presence of biochemical PCD hallmarks in germinating soybean seed coat and point to the involvement of the detected protease activities in processes such as reserve protein mobilization and weakening of seed coat.

Cytotoxic and molecular impacts of allelopathic effects of leaf residues of Eucalyptus globulus on soybean (Glycine max).

Eucalyptus trees litter plays a crucial role in structuring plant populations and regulating crop quality. To help characterize the allelopathic impact of Eucalyptus plantations and understand the interactions between tree litter and understorey plant populations, we performed two different genomic approaches to determine soybean (Glycine max) crop plant response to biotic stress induced by leaf residues of Eucalyptus globulus trees. For assessing cell death, a qualitative method of DNA fragmentation test (comet assay) was employed to detect cleavage of the genomic DNA into oligonucleosomal fragments and help to characterize the apoptotic event among the experimental samples. In addition, quantitative method of genome analysis at the transcriptional level also was conducted to investigate the expression responses of soybean genome to allelochemicals. Expression of specific genes, which are responsible for the breakdown of proteins during programmed cell death PCD (cysteine proteases and their inhibitors), was examined using semi-quantitative RT-PCR (sqPCR). Results of both conducted analyses proved significant genetic effects of Eucalyptus leaf residues on soybean crop genome, revealed by steady increase in DNA damage as well as variation in the transcript levels of cysteine proteases and inhibitors. Further detailed studies using more sensitive methods are necessary for a comprehensive understanding of the allelopathic effects of Eucalyptus plantations on crops.

Analysis of DNA instability in patients with periodontitis

Introduction: Periodontitis is characterized by loss of supporting connective tissue and alveolar bone around teeth. Although triggered by bacterial infection other factors such as apoptosis and immune mediators such as interleukin - 1 (IL-1), tumor necrosis factor alpha, IL-6, and receptor activator of NF-κB ligand have found to aggravate the periodontal disease prognosis. Apoptosis is believed to contribute to periodontal disease progression. Cleavage of chromosomal DNA into oligonucleosomal size fragments is an integral part of apoptosis. DNA fragmentation factor. (DFF) is a major apoptotic endonuclease representative of DNA fragmentation. DFF is responsible for DNA fragmentation, a hallmark event during apoptosis. Aim: This study aims to determine the presence of DNA instability in tissue samples of chronic periodontitis using double-stranded DNA marker using immunohistochemistry. Methodology: Tissue samples of five chronic periodontitis cases and one control case was obtained. Patients of any age and sex with clinically and histologically diagnosed cases of chronic periodontitis were selected. The tissue samples were subjected to immunohistochemical analysis using DFF. Results: Staining index of DFF 45 was calculated by multiplying staining intensity and the staining percentage. Two cases showed positive expression with staining index moderate in one case and low in one case. Three cases did not express DFF. Conclusion: Apoptosis plays a critical role in the regulation of inflammation and host immune response. Mild to moderate degree of DNA instability is found to be present in chronic periodontitis patients. The presence of DNA instability in chronic periodontitis emphasizes the importance of devising effective treatment modalities.

The Role of Vitamin D in Obesity and Diabetes: Ca2+ Signaling, Insulin Secretion, Adipocyte Apoptosis, and Bone Mineralization

Vitamin D has been linked to obesity and type 2 diabetes (T2D) in observational studies, and low vitamin D status is considered a risk factor for these interrelated diseases. However, mechanistic understanding of the role of vitamin D hormone, 1,25(OH)2‐vitamin D3, in obesity and T2D is lacking. We showed that 1,25(OH)2D3‐dependent cellular Ca2+ signals regulate apoptotic death of adipocytes and insulin secretion from pancreatic β‐cells (Sergeev, 2014, 2013, 2009, 2005, 2004). The anti‐obesity effects of 1,25(OH)2D3 in mature adipocytes are determined by its activity to generate, via multiple Ca2+ signaling pathways, a sustained increase in intracellular Ca2+ followed by activation of Ca2+‐dependent initiators and effectors of apoptosis. In pancreatic β‐cells, 1,25(OH)2D3 induces synchronous Ca2+ oscillations, which quantitatively, temporally and spatially pattern oscillatory insulin release from these cells. In recent studies, we examined the effects of increased intake of vitamin D and Ca in a mouse model of high fat diet‐induced obesity (DIO) on development of adiposity and diabetes. DIO mice were characterized by obese phenotype, elevated blood glucose and impaired glucose tolerance, increased insulin and decreased adiponectin concentrations in blood, decreased level of apoptosis in adipose tissue, and decreased Ca and P content in bone. Mice fed high fat diet (DIO) with high vitamin D3 and increased Ca content demonstrated a decreased weight of white adipose tissue depots and improved blood markers related to adiposity, T2D, and vitamin D status. Fasting plasma glucose and insulin concentrations in these mice were significantly decreased, approaching levels found in normal‐weight, non‐obese control, whereas adiponectin concentration demonstrated an increasing trend. DIO was accompanied by low vitamin D status (a decreased level of 25(OH)D) and a decreased plasma concentration of 1,25(OH)2D3. High vitamin D3 intake induced a significant increase in plasma concentrations of 25(OH)D and 1,25(OH)2D3, indicating high vitamin D nutritional status and normal vitamin D hormonal status. High vitamin D3 and Ca intakes were associated with induction of apoptosis (oligonucleosomal fragmentation and ssDNA breaks) and activation of Ca2+‐dependent apoptotic proteases (calpain and caspase‐12) in adipose tissue of DIO mice. High vitamin D3 and Ca intakes were effective in normalization (an increase) of mineral (Ca and P) content in the growing bone of DIO mice via regulatory effects mediated by 1,25(OH)2D3 ‐ PTH axis. The major results obtained demonstrate that increased vitamin D and Ca intake is highly effective in decreasing blood glucose and insulin in DIO and that the hormonal mechanism of this effect can involve 1,25(OH)2D3. Increasing vitamin D and Ca intakes in obesity also activates Ca2+‐mediated apoptotic pathway in adipocytes resulting in a decreased mass of fat tissue and improved markers of adiposity. Moreover, high vitamin D and Ca intakes improve bone status in obesity by increasing bone mineralization via PTH/1,25(OH)2D3‐mediated regulation. The findings obtained strongly imply that increasing vitamin D and Ca intakes may contribute to prevention of obesity, T2D, and bone disorders associated with these diseases.Support or Funding InformationSupported by USDA 2009‐35200‐05008 and SD00H533.

Response to cobalt toxicity in lichen Pseudevernia furfuracea; uptake, photosynthetic quantum yield, membrane integrity and deoxyribonucleic acid fragmentation

Objectives: This study aims to examine the toxic potential of Cobalt (Co) on photosystem II photosynthetic quantum yield, membrane integrity, and deoxyribonucleic acid (DNA) fragmentation formation. Materials and methods: Oligonucleosomal DNA fragmentation was detected by terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assay. Lipid peroxidation was determined with malondialdehyde analyzing. Results: The Fv/Fm ratio decreased in Pseudevernia furfuracea following exposure to various concentrations of Co (NO 3 ) 2 (5, 15 and 30 mM) for one, three and 24 hours. Co2+-treatment caused the accumulation of Co in lichen, induced severe oxidative stress by the generation of hydrogen peroxide, impaired the membrane integrity, and induced lipid peroxidation as measured by malondialdehyde. Samples treated with 15 mM and 30 mM of Co (NO3)2 had higher percentage of cell death than 5 mM-treated group. Conclusion: To our knowledge, this is the first study detecting a high rate of DNA fragmentation in situ in phycobiont layer of Pseudevernia furfuracea; while it reveals that mycobiont layer has a lower rate of TUNEL-positive cells. It has been concluded that Co exposure results in impaired photosynthesis accompanied by oxidative stress and DNA fragmentation in Pseudevernia furfuracea; all these effects were concentration-dependent.

Caspase-activated DNase Is Necessary and Sufficient for Oligonucleosomal DNA Breakdown, but Not for Chromatin Disassembly during Caspase-dependent Apoptosis of LN-18 Glioblastoma Cells

Caspase-dependent apoptosis is a controlled type of cell death characterized by oligonucleosomal DNA breakdown and major nuclear morphological alterations. Other kinds of cell death do not share these highly distinctive traits because caspase-activated DNase (DFF40/CAD) remains inactive. Here, we report that human glioblastoma multiforme-derived LN-18 cells do not hydrolyze DNA into oligonucleosomal fragments after apoptotic insult. Furthermore, their chromatin remains packaged into a single mass, with no signs of nuclear fragmentation. However, ultrastructural analysis reveals that nuclear disassembly occurs, although compacted chromatin does not localize into apoptotic nuclear bodies. Caspases become properly activated, and ICAD, the inhibitor of DFF40/CAD, is correctly processed. Using cell-free in vitro assays, we show that chromatin from isolated nuclei of LN-18 cells is suitable for hydrolysis into oligonuclesomal fragments by staurosporine-pretreated SH-SY5Y cytoplasms. However, staurosporine-pretreated LN-18 cytoplasms do not induce DNA laddering in isolated nuclei from either LN-18 or SH-SY5Y cells because LN-18 cells express lower amounts of DFF40/CAD. DFF40/CAD overexpression makes LN-18 cells fully competent to degrade their DNA into oligonucleosome-sized fragments, and yet they remain unable to arrange their chromatin into nuclear clumps after apoptotic insult. Indeed, isolated nuclei from LN-18 cells were resistant to undergoing apoptotic nuclear morphology in vitro. The use of LN-18 cells has uncovered a previously unsuspected cellular model, whereby a caspase-dependent chromatin package is DFF40/CAD-independent, and DFF40/CAD-mediated double-strand DNA fragmentation does not warrant the distribution of the chromatin into apoptotic nuclear bodies. The studies highlight a not-yet reported DFF40/CAD-independent mechanism driving conformational nuclear changes during caspase-dependent cell death.

Mitochondrial Uncoupling Protein 2 Induces Cell Cycle Arrest and Necrotic Cell Death

Uncoupling protein 2 (UCP2) is a mitochondrial membrane protein that regulates energy metabolism and reactive oxygen species (ROS) production. We generated mouse carboxy- and amino-terminal green fluorescent protein (GFP)-tagged UCP2 constructs to investigate the effect of UCP2 expression on cell proliferation and viability. UCP2-transfected Hepa 1-6 cells did not show reduced cellular adenosine triphosphate (ATP) but showed increased levels of glutathione. Flow cytometry analysis indicated that transfected cells were less proliferative than nontransfected controls, with most cells blocked at the G1 phase. The effect of UCP2 on cell cycle arrest could not be reversed by providing exogenous ATP or oxidant supply, and was not affected by the chemical uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP). However, this effect of UCP2 was augmented by treatment with genistein, a tyrosine kinase inhibitor, which by itself did not affect cell proliferation on control hepatocytes. Western blotting analysis revealed decreased expression levels of CDK6 but not CDK2 and D-type cyclins. Examination of cell viability in UCP2-transfected cells with Trypan Blue and Annexin-V staining revealed that UCP2 transfection led to significantly increased cell death. However, characteristics of apoptosis were absent in UCP2-transfected Hepa 1-6 cells, including lack of oligonucleosomal fragmentation (laddering) of chromosomal DNA, release of cytochrome c from mitochondria, and cleavage of caspase-3. In conclusion, our results indicate that UCP2 induces cell cycle arrest at G1 phase and causes nonapoptotic cell death, suggesting that UCP2 may act as a powerful influence on hepatic regeneration and cell death in the steatotic liver.

New heterocyclic chalcones. Part 6. Synthesis and cytotoxic activities of 5- or 6-(3-aryl- 2-propenoyl)-2(3H)-benzoxazolones

Abstract A number of chalcones bearing an oxazole cycle were synthesized by Claisen-Schmidt condensation of 5-acetyl-2(3H)-benzoxazolone or 6-acetyl-2(3H)-benzoxazolone and the appropriate aldehydes. The chalcones were evaluated for cytotoxic activity against several tumor cell lines – BV-173 (human B cell precursor leukemia), MCF-7 and MDA-MB-231 (human breast adenocarcinoma) using the MTT-dye reduction assay. The tested compounds exhibit concentration-dependent cytotoxic effects at micromolar concentrations. Exposure of the BV-173 tumor cell line to compound 3f results in strong mono- and oligonucleosomal fragmentation of genomic DNA, as evidenced by a ‘cell death detection’ ELISA kit, which unambiguously indicates that the induction of apoptosis is implicated in the cytotoxic mode of action of the tested compound.

Differential expression of long non-coding RNAs during genotoxic stress-induced apoptosis in HeLa and MCF-7 cells

Long non-coding RNAs (lncRNAs) are emerging as new players in cancer as they are implicated in diverse biological processes and aberrantly expressed in a variety of human cancers. No data are available on their function under genotoxic stress-induced apoptosis. In this work, we assessed the behavior of some candidate lncRNAs (HOTAIR, MALAT1, TUG1, lincRNA-p21, GAS5, MEG3, PANDA, UCA1, ANRIL, and CCND1) during DNA damage-induced cell death in HeLa and caspase-3-deficient MCF-7 cells using bleomycin (BLM) and γ-radiation to induce DNA damage. Cells were incubated in the presence of BLM for 24h or irradiated. Apoptosis was analyzed by measurement of oligonucleosomal fragmentation of nuclear DNA. Our results reveal that basal RNA expression levels as well as the changes in the lncRNA expression rates during genotoxic stress-induced apoptosis were cell-type and/or DNA-damaging agent-specific. Generally, we found that some of the RNA molecules (HOTAIR and MALAT1) are down-regulated while many of them (lincRNA-p21, GAS5, MEG3, ANRIL, and ncRNA-CCND1) are up-regulated and some others (TUG1, UCA1, and PANDA) not affected. The decline in the expression of HOTAIR (approx. twofold, p<0.01) and MALAT1 (approx 1.6-fold, p<0.01) was clearly evident in BLM-treated HeLa and MCF cells (only HOTAIR, fivefold, p<0.01). For lincRNA-p21, ncRNA-CCND1, and MEG3, a similar up-regulation pattern was obvious in both cell lines where the increase was generally more pronounced in BLM-treated cells. Interestingly, the induction of ANRIL and GAS5 was mainly restricted to irradiated cells. In conclusion, our findings reveal a differential regulation of individual lncRNAs during genotoxic stress-induced apoptosis.

Apoptotic DNA Degradation into Oligonucleosomal Fragments, but Not Apoptotic Nuclear Morphology, Relies on a Cytosolic Pool of DFF40/CAD Endonuclease

Apoptotic cell death is characterized by nuclear fragmentation and oligonucleosomal DNA degradation, mediated by the caspase-dependent specific activation of DFF40/CAD endonuclease. Here, we describe how, upon apoptotic stimuli, SK-N-AS human neuroblastoma-derived cells show apoptotic nuclear morphology without displaying concomitant internucleosomal DNA fragmentation. Cytotoxicity afforded after staurosporine treatment is comparable with that obtained in SH-SY5Y cells, which exhibit a complete apoptotic phenotype. SK-N-AS cell death is a caspase-dependent process that can be impaired by the pan-caspase inhibitor q-VD-OPh. The endogenous inhibitor of DFF40/CAD, ICAD, is correctly processed, and dff40/cad cDNA sequence does not reveal mutations altering its amino acid composition. Biochemical approaches show that both SH-SY5Y and SK-N-AS resting cells express comparable levels of DFF40/CAD. However, the endonuclease is poorly expressed in the cytosolic fraction of healthy SK-N-AS cells. Despite this differential subcellular distribution of DFF40/CAD, we find no differences in the subcellular localization of both pro-caspase-3 and ICAD between the analyzed cell lines. After staurosporine treatment, the preferential processing of ICAD in the cytosolic fraction allows the translocation of DFF40/CAD from this fraction to a chromatin-enriched one. Therefore, the low levels of cytosolic DFF40/CAD detected in SK-N-AS cells determine the absence of DNA laddering after staurosporine treatment. In these cells DFF40/CAD cytosolic levels can be restored by the overexpression of their own endonuclease, which is sufficient to make them proficient at degrading their chromatin into oligonucleosome-size fragments after staurosporine treatment. Altogether, the cytosolic levels of DFF40/CAD are determinants in achieving a complete apoptotic phenotype, including oligonucleosomal DNA degradation.

Antileishmanial activity of cryptolepine analogues and apoptotic effects of 2,7-dibromocryptolepine against Leishmania donovani promastigotes

Cryptolepine (5-methyl-10H-indolo [3, 2-b] quinoline), an indoloquinoline alkaloid (1) isolated from a medicinal plant traditionally used in Western Africa for treatment of malaria, has been shown to possess broad spectrum biological activity in addition to its antiplasmodial effect. Here, the antileishmanial properties of 11 synthetic derivatives of cryptolepine against Leishmania donovani parasites have been evaluated for the first time. 2,7-Dibromocryptolepine (8; IC50 0.5 ± 0.1 μM) was found to be the most active analogue against the promastigote form of a classical L. donovani strain (AG83) in comparison to the natural alkaloid, cryptolepine (1; IC50 1.6 ± 0.1 μM). Further, 8 was found to substantially inhibit the intracellular amastigote forms of two clinical isolates, one of them being an SbV-resistant strain of L. donovani. Moreover, the toxicity of 8 against normal mouse peritoneal macrophage cells was markedly lower than that of 1 (IC50 values: 9.0 ± 1.2 and 1.1 ± 0.3 μM, respectively), indicating 8 to be a prospective “lead” towards novel antileishmanial therapy. This was supported by studies on the mechanism of cytotoxicity induced by 8 in L. donovani promastigotes (AG83), which revealed the cytoplasmic and nuclear features of metazoan apoptosis. Light microscopic observation demonstrated a gradual decline in the motility, cell volume, and survival of the treated parasites with increasing incubation time. Flow cytometric analysis of phosphatidylserine externalization and distribution of cells in different phases of cell cycle confirmed the presence of a substantial percentage of cells in early apoptotic stage. Disruption of mitochondrial membrane integrity in terms of depolarization of membrane potential, and finally degradation of chromosomal DNA into oligonucleosomal fragments - the hallmark event of apoptosis - characterized the mode of cell death in L. donovani promastigotes.

Presence of base excision repair enzymes in the wheat aleurone and their activation in cells undergoing programmed cell death

Cereal aleurone cells are specialized endosperm cells that produce enzymes to hydrolyze the starchy endosperm during germination. Aleurone cells can undergo programmed cell death (PCD) when incubated in the presence of gibberellic acid (GA) in contrast to abscisic acid (ABA) which inhibits the process. The progression of PCD in aleurone layer cells of wheat grain is accompanied by an increase in deoxyribonuclease (DNase) activities and the internucleosomal degradation of nuclear DNA. Reactive oxygen species (ROS) are increased during PCD in the aleurone cells owing to the β-oxidation of triglycerides and inhibition of the antioxidant enzymes possibly leading to extensive oxidative damage to DNA. ROS generate mainly non-bulky DNA base lesions which are removed in the base excision repair (BER) pathway, initiated by the DNA glycosylases. At present, very little is known about oxidative DNA damage repair in cereals. Here, we study DNA repair in the cell-free extracts of wheat aleurone layer incubated or not with phytohormones. We show, for the first time, the presence of 8-oxoguanine-DNA and ethenoadenine-DNA glycosylase activities in wheat aleurone cells. Interestingly, the DNA glycosylase and AP endonuclease activities are strongly induced in the presence of GA. Based on these data we propose that GA in addition to activation of nuclear DNases also induces the DNA repair activities which remove oxidized DNA bases in the BER pathway. Potential roles of the wheat DNA glycosylases in GA-induced oligonucleosomal fragmentation of DNA and metabolic activation of aleurone layer cells via repair of transcribed regions are discussed.

Dihydroartemisinin induces caspase-8-dependent apoptosis in murine GT1-7 hypothalamic neurons

The cytotoxicity of dihydroartemisinin (DHART; an active metabolite of artemisinin or ART) was investigated using murine GT1-7 hypothalamic neurons. A decrease in neuronal cell viability was observed in DHART-treated cells typically after 6 h of incubation. When neuronal cells were exposed to DHART for 24 h, the value of IC50 was found to be 24 ± 3.2 µM (n = 6). Based on acridine orange/ethidium bromide (dual) staining and increases in oligonucleosomal fragmentation, the cell death at lower concentrations of DHART (≤20 µM) was suggestive of apoptotic in nature. On the other hand, at higher concentrations of DHART (≥50 µM), the cell death appeared to be predominantly necrotic. A potentiation of cytotoxic effects was seen in Fe(II)-containing medium whereas inclusion of deferoxamine (chelator of Fe) attenuated such effects. This would imply that the cleavage of the endoperoxide bridge of DHART by Fe(II) and the subsequent formation of O- and C-centered radical(s) are important determinants of the cytotoxicity that was observed. The activities of caspase-3/7, caspase-8 and caspase-9 were maximally seen at 12-h after exposure to DHART. Inhibitors of caspase-8 (C8I) but not caspase-9 (C9I) reduced the DHART-induced increase in caspase-3/7 activity. A relatively higher activity of caspase-8 to that of caspase-9 and the inhibition of caspsase-3/7 activity by C8I suggest that DHART induces caspase-8-mediated apoptosis involving the extrinsic pathway. Taken together, this study demonstrates that DHART and, possibly, other ART derivatives have considerable neurotoxic potential and facilitate our understanding of these agents.