DNA and cell death

The type of DNA damage and the role of poly (ADP-ribosyl) polymerase (ADPRP) and sulphated glyprotein 2 (SGP-2) in programmed cell death (apoptosis) was investigated in the following model systems: i) rat thymocytes treated with dexamethasone (DEX) eitherin vitro orin vivo; ii) human perypheral blood mononuclear cells (hPBMCs) exposed to oxygen free radicals (OR); iii) K562 cell line killed by hPBCs during spontaneous (NK) or interleukin-2 (IL-2)-induced (LAK) cytotoxic activity. The results suggest that ADPRP and SGP-2 are involved in the apoptotic process, but their role probably differs according to the type of cell and the inducing damage/stimulus. Moreover, no simple correlation appears to exist between the extent of DNA damage and cell survival or cell death.     

Characterization of cells with different mitochondrial membrane potential during apoptosis.

BACKGROUND: Until now, the simultaneous analysis of several parameters during apoptosis, including DNA content and mitochondrial membrane potential (DeltaPsi), has not been possible because of the spectral characteristics of the commonly used dyes. Using polychromatic flow cytometry based upon multiple laser and UV lamp excitation, we have characterized cells with different DeltaPsi during apoptosis. METHODS: U937 cells were treated with the flavonoid quercetin (Qu) and stained with JC-1 to detect DeltaPsi, propidium iodide (PI) for cell viability, Hoechst 33342 for DNA content, Annexin V conjugated with Alexa Fluor-647 for detection of phosphatidilserine (PS) exposure, marker of early apoptosis, or Mitotracker Deep Red for the determination of mitochondrial mass. RESULTS: Treatment with Qu provoked the onset of three cell populations with different DeltaPsi: (1) healthy cells, with normal DeltaPsi, DNA content and physical parameters, high mitochondrial mass, PI- and Annexin V-negative; (2) cells with intermediate DeltaPsi and normal DNA content, but with physical parameters typical of apoptotic cells and low mitochondrial mass; most of them were PI+ and Annexin V+; (3) cells with collapsed DeltaPsi that had low mitochondrial mass and were Annexin-V+, PI+; half of them showed diminished DNA content. Similar results, i.e. the presence of cells with intermediate DeltaPsi, were observed in other models of apoptosis. CONCLUSIONS: During Qu-induced apoptosis, loss of DeltaPsi, PS exposure, and decrease of mitochondrial mass are early events that precede permeability to PI and loss of DNA. Populations of cells with different DeltaPsi, as revealed by flow cytometry after JC-1 staining, differed also for other parameters associated to apoptosis. Thus, the simultaneous analysis of several parameters by polychromatic flow cytometry permits a better identification of many stages of cell death, and, more in general, allows to evaluate the eventual heterogenic sensibility of the population under study to a given compound.     

Apoptosis-resistant phenotype in HL-60-derived cells HCW-2 is related to changes in expression of stress-induced proteins that impact on redox status and mitochondrial metabolism

The onset of resistance to drug-induced apoptosis of tumour cells is a major problem in cancer therapy. We studied a drug-selected clone of promyelocytic HL-60 cells, called HCW-2, which display a complex resistance to a wide variety of apoptosis-inducing agents and we found that these cells show a dramatic increase in the expression of heat shock proteins (Hsps) 70 and 27, while the parental cell line does not. It is known that stress proteins such as Hsps can confer resistance to a variety of damaging agents other than heat shock, such as TNF-alpha, monocyte-induced cytotoxicity, and also play a role in resistance to chemotherapy. This elevated expression of Hsps is paralleled by an increased activity of mitochondrial metabolism and pentose phosphate pathway, this latter leading to high levels of glucose-6-phosphate dehydrogenase and, consequently, of glutathione. Thus, the apoptotic-deficient phenotype is likely because of the presence of high levels of stress response proteins and GSH, which may confer resistance to apoptotic agents, including chemotherapy drugs. Moreover, the fact that in HCW-2 cells Hsp70 are mainly localised in mitochondria may account for the increased performances of mitochondrial metabolism. These observations could have some implications for the therapy of cancer, and for the design of combined strategies that act on antioxidant defences of the neoplastic cell.     

Genetic polymorphisms of Fas (CD95) and FasL (CD178) in human longevity: studies on centenarians

Apoptosis plays a crucial role in immunosenescence, as also evidenced by the increased expression of Fas in lymphocytes from aged people. However, little is known about the genetic regulation of Fas and its ligand, FasL. We have studied their polymorphisms in 50 centenarians and 86 young donors living in Northern Italy. The first Fas polymorphism, at position -670, has in Caucasian a heterozigosity of 51%; the second, at -1377 position, has the wild type allele (G) with a very high frequency (83%) respect to the mutant allele. Genotype and allele distribution for both polymorphisms were similar in controls and centenarians. Similar results were found as far as two FasL polymorphisms (IVS2nt-124 and IVS3nt169) are concerned. On the whole, our data suggest that Fas and FasL polymorphisms, as well as their haplotypes, are unlikely to be associated with successful human longevity.     

Changes in intramitochondrial cardiolipin distribution in apoptosis-resistant HCW-2 cells, derived from the human promyelocytic leukemia HL-60

Using a cytofluorimetric approach, we studied intramitochondrial cardiolipin (CL) distribution in HCW-2 cells, an apoptosis-resistant clone of human HL-60 cells. In HL-60, about 50% of total CL is distributed in the outer leaflet of mitochondrial inner membrane, while in HCW-2 a significantly higher amount of CL (about 65%) is in that site. In basal conditions, HSW-2 cells also show a reduced mitochondrial membrane potential even if they are able to proliferate as the parental line. Taking into account the complex functions that CL plays in the regulation of mitochondrial activity, it is likely that HCW-2 could produce ATP utilizing more glycolytic pathways rather than mitochondrial respiratory chain.     

Mitochondrial heterogeneity during staurosporine-induced apoptosis in HL60 cells: analysis at the single cell and single organelle level

BACKGROUND: Apoptosis is a complex phenomenon during which several events occur. A growing interest exists on the role and functionality of mitochondria during this type of cell death. The responsibility of modifications in mitochondrial membrane potential (Delta Psi) in triggering apoptosis is under investigation. METHODS: We evaluated Delta Psi changes in HL60 cells treated with staurosporine (STS). Flow cytometry and confocal microscopy have been used to analyze samples stained with two Delta Psi-sensitive probes, JC-1 and MitoTrackertrade mark Red CMXRos. RESULTS: At the cellular level, we found heterogeneic behavior. Indeed, after STS treatment, some cells displayed typical markers of apoptosis and a collapse in Delta Psi. Others were apoptotic with no changes in Delta Psi, others changed Delta Psi without being apoptotic, and others were healthy. The same heterogeneic response to STS was found at the single organelle level. In a given cell, some mitochondria were depolarized whereas others were not. CONCLUSION: In this model of apoptosis, changes in Delta Psi can be different among cells of the same type and among different organelles of the same cell. The collapse in Delta Psi is thus a heterogeneic phenomenon that seems to be an ancillary event following the irreversible phase of the apoptotic process.     

Ex Vivo Effect of Varespladib on Secretory Phospholipase A2 Alveolar Activity in Infants with ARDS

Background

Secretory phospholipase A2 (sPLA2) plays a pivotal role in acute respiratory distress syndrome (ARDS). This enzyme seems an interesting target to reduce surfactant catabolism and lung tissue inflammation. Varespladib is a specifically designed indolic sPLA2 inhibitor, which has shown promising results in animals and adults. No specific data in pediatric ARDS patients are yet available.

Methods

We studied varespladib in broncho-alveolar lavage (BAL) fluids obtained ex vivo from pediatric ARDS patients. Clinical data and worst gas exchange values during the ARDS course were recorded. Samples were treated with saline or 10–40–100 µM varespladib and incubated at 37°C. Total sPLA2 activity was measured by non-radioactive method. BAL samples were subjected to western blotting to identify the main sPLA isotypes with different sensitivity to varespladib. Results was corrected for lavage dilution using the serum-to-BAL urea ratio and for varespladib absorbance.

Results

Varespladib reduces sPLA2 activity (p<0.0001) at 10,40 and 100 µM; both sPLA2 activity reduction and its ratio to total proteins significantly raise with increasing varespladib concentrations (p<0.001). IC₅₀ was 80 µM. Western blotting revealed the presence of sPLA2-IIA and –IB isotypes in BAL samples. Significant correlations exist between the sPLA2 activity reduction/proteins ratio and PaO₂ (rho = 0.63;p<0.001), PaO₂/FiO₂ (rho = 0.7; p<0.001), oxygenation (rho = −0.6; p<0.001) and ventilation (rho = −0.4;p = 0.038) indexes.

Conclusions

Varespladib significantly inhibits sPLA2 in BAL of infants affected by post-neonatal ARDS. Inhibition seems to be inversely related to the severity of gas exchange impairment.     

Summary of the 2000 Surgeon General's Listening Session: Toward a National Action Plan on Overweight and Obesity

Objective: To provide insight into discussions at the Surgeon General's Listening Session, “Toward a National Action Plan on Overweight and Obesity,” and to complement The Surgeon General's Call to Action to Prevent and Decrease Overweight and Obesity. Research Methods and Procedures: On December 7 and 8, 2000, representatives from federal, state, academic, and private sectors attended the Surgeon General's Listening Session and were given an opportunity to recommend what to include in a national plan to address overweight and obesity. The public was invited to comment during a corresponding public comment period. The Surgeon General's Listening Session was also broadcast on the Internet, allowing others to view the deliberations live or access the archived files. Significant discussion points from the Listening Session have been reviewed by representatives of the federal agencies and are the basis of this complementary document. Results: Examples of issues, strategies, and barriers to change are discussed within five thematic areas: schools, health care, family and community, worksite, and media. Suggested cooperative or collaborative actions for preventing and decreasing overweight and obesity are described. An annotated list of some programmatic partnerships is included. Discussion: The Surgeon General's Listening Session provided an opportunity for representatives from family and community groups, schools, the media, the health-care environment, and worksites to become partners and to unite around the common goal of preventing and decreasing overweight and obesity. The combination of approaches from these perspectives offers a rich resource of opportunity to combat the public health epidemic of overweight and obesity.