Immunological approach to investigating membrane cell damages induced by lipoperoxidative stress. Application to far UV-irradiated erythrocytes

Differential cytotoxicity of MEX: a component of Neem oil whose action is exerted at the cell membrane level

Neem oil is obtained from the seeds of the tree Azadirachta indica. Its chemical composition is very complex, being rich in terpenoids and limonoids, as well as volatile sulphur modified compounds. This work focused on the evaluation of a component of the whole Neem oil obtained by methanolic extraction and defined as MEX. Cytotoxicity was assessed on two different cell populations: a stabilized murine fibroblast line (3T6) and a tumor cell line (HeLa). The data presented here suggest a differential sensitivity of these two populations, the tumor line exhibiting a significantly higher sensitivity to MEX. The data strongly suggest that its toxic target is the cell membrane. In addition the results presented here imply that MEX may contain one or more agents that could find a potential use in anti-proliferative therapy.

The cellular concentration of Bcl-2 determines its pro- or anti-apoptotic effect

Bcl-2 is an oncoprotein that is widely known to promote cell survival by inhibiting apoptosis. We explored the consequences of different expression paradigms on the cellular action of Bcl-2. Using either transient or stable transfection combined with doxycycline-inducible expression, we titrated the cellular concentration of Bcl-2. With each expression paradigm Bcl-2 was correctly targeted to the endoplasmic reticulum and mitochondria. However, with protocols that generated the greatest cellular concentrations of Bcl-2 the structure of these organelles was dramatically altered. The endoplasmic reticulum appeared to be substantially fragmented, whilst mitochondria coalesced into dense perinuclear structures. Under these conditions of high Bcl-2 expression, cells were not protected from pro-apoptotic stimuli. Rather Bcl-2 itself caused a significant amount of spontaneous cell death, and sensitised the cells to apoptotic agents such as staurosporine or ceramide. We observed a direct correlation between Bcl-2 concentration and spontaneous apoptosis. Expression of calbindin, a calcium buffering protein, or an enzyme that inhibited inositol 1,4,5-trisphosphate-mediated calcium release, significantly reduced cell death caused by Bcl-2 expression. We further observed that high levels of Bcl-2 expression caused lipid peroxidation and that the deleterious effects of Bcl-2 could be abrogated by the reactive oxygen species (ROS) scavenger Trolox. When stably expressed at low levels, Bcl-2 did not corrupt organelle structure or trigger spontaneous apoptosis. Rather, it protected cells from pro-apoptotic stimuli. These data reveal that high cellular concentrations of Bcl-2 lead to a calcium- and ROS-dependent induction of death. Selection of the appropriate expression paradigm is therefore crucial when investigating the biological role of Bcl-2.

Production and specificity of polyclonal antibodies to hexanal-lysine adducts

Hexanal content is a widely used index of lipid oxidation in foods. The objectives of this study were to develop antibodies to hexanal-lysine adducts, devise an ELISA, and characterize antibody specificity. Hexanal was made immunogenic by covalent attachment to lysine side chains of bovine serum albumin via reductive alkylation. Polyclonal antibodies had antiserum titers as high as 6.15 x 10(5). A competitive indirect ELISA was developed with a detection limit of 0.7 ng of hexanal/mL. Antibodies were carrier-independent, reacting with hexanal conjugates of several proteins but not with the corresponding native proteins. Cross-reactivities with chicken serum albumin conjugates of n-heptanal, n-pentanal, and n-octanal were 86. 3, 11.8, and 2.2%, respectively. Antibodies reacted strongly with hexanal-modified lysine and hexanal-modified epsilon-aminocaproic acid but did not recognize free amino acids or free hexanal. It may be feasible to use this ELISA to monitor lipid oxidation in food provided hexanal is alkylated to a carrier protein prior to analysis.

Heme oxygenase induction by UVA radiation. A response to oxidative stress in rat liver

Heme oxygenase is a key enzyme for heme catabolism and catalyzes the oxidative degradation of heme to form biliverdin IX alpha, an immediate precursor of bilirubin. In order to shed light on the mechanism by which UVA radiation causes oxidative damage, the relationship between heme oxygenase induction and oxidative stress was studied. HO-1 activity, lipid peroxidation and generation of active oxygen species (H2O2) were measured in rat liver exposed to UVA radiation. Besides, soluble and enzymatic antioxidant defenses (GSH, SOD, CAT and GSH-Px) were determined, while bilirubin antioxidant capacity was also evaluated. UVA radiation markedly increased both lipid peroxidation (180% +/- 7; S.E.M., n = 9 over control value of 0.1 +/- 0.01 nmol MDA/min per mg prot.) and steady state concentration of hydrogen peroxide (4 +/- 0.03 microM; S.E.M., n = 9) 3 h after treatment. At the same time, GSH content decreased to 3.6 +/- 0.2 mumol/g liver (S.E.M., n = 9) increasing thereafter. Antioxidant enzymes reached minimum values 6 h after UVA treatment (SOD: 7.2 +/- 0.2 U/mg protein, CAT: 7.8 +/- 0.2 pmol/mg protein, GSH-Px: 0.088 +/- 0.004 U/mg protein; S.E.M., n = 9), starting to increase 12 h after irradiation. HO-1 induction was observed 6 h after UVA irradiation, reaching a maximum value of 2.5 +/- 0.03 U/mg protein (S.E.M., n = 9) 12 h after treatment, and then declined until it reached control levels 24 h after exposure. Administration of bilirubin 2 h before UVA irradiation, entirely prevented HO-1 induction, the increase in MDA content and the decrease in GSH levels. This study shows that UVA irradiation leads to oxidative stress as evidenced by increased MDA content and H2O2 steady state levels, and depletion of GSH, SOD, CAT and GSH-Px. All these changes produced HO-1 induction. It is concluded that the induction of this enzyme could be a response to oxidative stress, since bilirubin can act as a physiological antioxidant.