The effect of melittin, an activator of phospholipase A 2 , on proliferation and death of rat thymocytes in a broad concentration range was studied. Cell proliferation was estimated by the accumulation of colchicin metaphases, necrotic death was determined from lysis and staining of cells with trypan blue, and apoptosis was assessed from the type of DNA fragmentation, the amount of fragmented DNA, and the percentage of cells with subdiploid DNA. It was shown that low melittin concentrations (below 5 ug/ml) stimulate thymocyte proliferation. At high melittin concentrations, thymocytes die by the primary necrosis type. Throughout the concentration range studied, melittin does not produce apoptosis in thymocytes. Conversely, high melittin concentrations even inhibit thymocyte apoptosis in the control and after irradiation. An inhibitor of RNA synthesis actinomycin D does not affect thymocyte death in the presence of melittin. It is concluded that the activation of phospholipase A 2 can induce necrosis but not apoptosis and thus is not a necessary step in the signaling cascade that initiates apoptosis in thymocytes.

The effect of inhibitors of arachidonic acid metabolism on proliferation and death of tumor P-388 cells in a broad concentration range was studied. Cell proliferation was estimated by the metaphase frequency and the proportion of cells in S phase; cell death was determined from lysis, staining of cells with trypan blue, nuclear damage, percentage of cells with subdiploid DNA and the type of DNA fragmentation. It was shown that low concentrations of phospholipase A P and lipoxygenase inhibitors stimulated the proliferation of P-388 cells. At higher concentrations, the inhibitors suppressed cell proliferation by blocking the G I -S transition and induced cell death of the apoptosis type. Indomethacin, an inhibitor of cyclooxygenase, did not initiate cell death, nor did it affect the proliferation of P-388 cells at concentrations of up to 10 W WM. z 1998 Federation of European Biochemical Societies.

The effects of avermectins on radiation-and dexamethasone-induced apoptosis of rat thymocytes have been studied. In particular, the properties of abamectin (avermectin B 1 ), ivermectin (22,23-dihydroavermectin B 1 , H 2 B 1 ) and aversectin C were examined. Aversectin C is a mixture of eight naturally occurring avermectins of the following composition: B 1 (42%), B 2 (22%), A 1 (13%) and A 2 (23%). This mixture is currently widely used as active ingredient in veterinary antiparasitic formulations produced by Pharmbiomed Co. Apoptosis was estimated by membrane damage, nuclear pycnosis (or chromatin condensation), DNA fragmentation and percentage of cells with subdiploid DNA. It was shown that aversectin C inhibits thymocyte apoptosis induced by both agents. The IC 50 dose was in the range of 0.1-0.3 µg/ml for aversectin C, whereas abamectin and ivermectin produced no effect up to 1 µg/ml. It is suggested that avermectins of the A series are responsible for the high anti-apoptotic activity exhibited by aversectin C. Thus, aversectin C is not only an effective antiparasitic drug but is also capable of exhibiting some other useful activities, e.g. a cytoprotective effect exerted on the mammalian immune cells. Avermectins, antiparasitic drugs, apoptosis, thymocytes, dexamethasone, gamma raysThe avermectins are a family of closely related 16-membered macrocyclic lactones produced by the fungus Streptomyces avermitilis. Nearly all the avermectins exhibit a broad spectrum of activity against nematode and arthropode parasites, with the B 1a compound being the most potent (Campbell 1989). Accordingly, it was used as active ingredient in commercial antiparasitic formulations. Until recently, there were basically two types of such avermectin-based active ingredients, i.e. ivermectin (consisting mainly of avermectin H 2 B 1a ) and abamectin (predominantly containing avermectin B 1a ). However, several years ago the Pharmbiomed Co. started manufacturing the veterinary and plant protection formulations based on a new active ingredient -aversectin C which is an intrinsic mixture of eight naturally occurring avermectins. Preliminary experiments demonstrated that aversectin C (presumably due to the presence of avermectins of both the A-and B-series) possesses some new useful features compared to ivermectin and abamectin, e.g. with the same high efficacy, the spectrum of activity is broader, level of residues is lower and, hence, the shorter withdrawal periods could be recommended (Simetsky et al. 1994;Berezkina et al. 1996). Furthermore, degradation of aversectin C in soil and water was found to be more effective compared to abamectin and ivermectin ( M o sin et al. 1998) and, hence, ecologically aversectin C is safer.

We studied changes in ROS content in the aorta of Wistar rats at early terms after irradiation in doses equal to single fraction used in tumor radiotherapy and the effects of taxifolin and fucoidin, blockers of leukocyte adhesion to endothelium, on ROS content. Male rats were exposed to X-rays (200 kW) in doses of 1-7.5 Gy. ROS production in aorta segments was measured in 1-48 h after irradiation by dichlorodihydrofluorescein oxidation. The content of ROS in the aorta of rats exposed to radiation in doses of 1-2.5 Gy increased in 1-24 h after irradiation, the peak ROS content was found in 2 h after irradiation. Taxifolin (100 μg/kg dihydroquercetin once a day with drinking water) and fucoidin (10 mg/kg, i.v.) abolished ROS accumulation. The content of ROS in rat aorta increased in 1-24 h after irradiation in doses used for tumor radiotherapy and this increase can be determined by leukocyte adhesion to the endothelium.

The effect of the interaction of different types of cells on the interphase death and pycnosis of thymocytes irradiated in vitro was studied. When removed from the thymus suspension of cells with natural killer activity, medullary thymocytes and macrophages did not change the radiation-induced death of cortical thymocytes. On the other hand, postirradiation incubation of cortical thymocytes together with unirradiated thymocytes or with cells of certain other cell lines diminished thymocyte death. Mixing the cell suspensions and changing the incubation medium decreased thymocyte death. All of these results indicate that these cells produce soluble mediators that are toxic to the cells that secrete them. The possible nature of these autotoxic mediators has been studied using inhibitors of arachidonic acid metabolism. Inhibitors of phospholipase A2 or lipoxygenase reduced interphase death markedly, while an inhibitor of cyclooxygenase did not. These data suggest that some lipoxygenase products may serve as autotoxic mediators in the interphase death of thymocytes.

No abstract

The values of the oxygen effect (m) and the maximal protective effect of cysteamine (DMF*) were estimated for four Escherichia coli strains: AB1157 (wild type), AB1886 (uvrA), AB2463 (recA), and p3478 (polA). A correlation made between DMF* and m as well as the kinetics of the increase of DMF with oxygen depletion showed that the protective effect of cysteamine is realized by three mechanisms: (i) anoxia achieved by oxygen reduction, with the DMF varying from 2.2 to 4.2 for different E. coli strains (this protection is the major contribution to the entire mechanism); (ii) lowering of the indirect radiation effect; i.e., for 50 mM cysteamine DMF does not exceed 1.1; and (iii) increase of the efficiency of enzymatic repair. The latter effect of cysteamine is registered only with the wild-type E. coli, the DMF being not less than 1.4.

We studied the effect of lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA) and fungus Lecanicillum lecanii extract on lymphatic leukemia P388 cells. The cells grown in the abdominal cavity of DBA2 mice for 7 days were transferred into a nutrient medium. The effect of lipoxygenase inhibitors was evaluated by changes in cell number, trypan blue staining, nucleus damage, and changes in cell distribution by DNA content after 22-h incubation. NDGA and fungus extract induced apoptotic death of lymphatic leukemia cells, which was seen from nucleus damage and reduced DNA content in cells. IC for NDGA and fungus extract was 0.66 and 5.5 μg/ml, respectively.