Elevation of circulating NO: its effects on hemodynamics and vascular smooth muscle cell proliferation in rats.

Object of our study was to characterize the effects of elevated circulating NO on hemodynamics and vascular smooth muscle cell proliferation in rats. Administration of molsidomine (10, 25, 50 mg/kg, bid p.o.) was followed by pharmacodynamic effects: elevation of plasma nitrite/nitrate levels and reduction of blood pressure (25 and 50 mg/kg, bid p.o.). Under these conditions no antiproliferative activity occurred in a model of "air dried" carotid artery injury. From these results we conclude that NO does not act as an antiproliferative agent under conditions where smooth muscle cell injury predominates.

Immunomodulatory effects of ultra-low-dose interleukin-2 in cancer patients: a phase-IB study.

High-dose interleukin-(IL-2) has been broadly studied in tumor therapy, yet it may be inhibitory to T-cell-dependent immunity. Therefore immune and tumour responses mediated by low-dose IL-2 were studied systematically with respect to the feedback organisation of immune responses. IL-2 was administered once daily at three dose levels: 0.18, 0.9, 4.5 MIU/m2 according to three different schedules requiring subcutaneous (s.c.) injection once weekly (four doses, stratum I), thrice weekly every other day (nine doses, stratum II), or five times weekly every other week (ten doses, stratum III). A total of 46 patients with advanced cancer were randomly assigned to one of the nine treatment groups. Systemic effects were induced at doses as low as 0.18 MIU/m2 IL-2 s.c. as demonstrated from measurable IL-2 serum levels, induction of circulating IL-6, a transient lymphopenia, and stimulation of delayed-type hypersensitivity (DTH) responses of the skin. Analysis of the different IL-2 schedules demonstrated (a) prolonged effects of once-weekly injections on DTH responses, lymphocyte and eosinophil counts, and (b) maximum increase of eosinophil counts and preferential expansion of activated NK cells with repeated injections every 48 h or 72 h (stratum II), while sequential treatment according to stratum III was found to be more potent in increasing the number of activated T cells. A tumour response was observed in 1/15 patients with renal cell carcinoma who experienced more than 50% tumour regression for 8 months; 12 patients had stable disease for 4 months (median). These data demonstrate prolonged immunological effects of ultra-low doses of s.c. IL-2 despite its short half-life. Furthermore, scheduling of IL-2 was found to affect immune responsiveness specifically as demonstrated by the differential effects on natural killer and T cell populations.

Low levels of hydrogen peroxide enhance platelet aggregation by cyclooxygenase activation.

Platelet aggregation can be triggered by addition of exogenous arachidonate owing to its conversion to endoperoxides and thromboxane A2. The dose-response curve of arachidonate-induced platelet aggregation exhibited a very steep slope. Simultaneous addition of H2O2 (1-200 microM) significantly shifted this curve to the left. H2O2 alone did not induce aggregation up to a concentration of 1 mM; however, a reversible increase of cytoplasmic Ca2+ and a small increase of the thromboxane levels could be observed. In the presence of exogenous arachidonate H2O2 led to an increased formation of arachidonate metabolites. Our data demonstrate that at threshold levels of 20:4 H2O2 is able to promote conversion of 20:4 to proaggregatory prostaglandin endoperoxides, and subsequently platelet activation is facilitated. Thus we support the evidence for a role of H2O2 in the activation of cyclooxygenase possibly by providing an adequate peroxide tone.

Cytotoxic enzyme release and oxygen centered radical formation in human neutrophils are selectively inhibited by E-type prostaglandins but not by PGI2.

The action of PGE1, PGE2, PGI2 and iloprost on superoxide anion generation, lysosomal enzyme release, and changes of Ca2+ fluxes in human polymorphonuclear leukocytes (PMN) was studied in vitro. Both PGE-type compounds were equipotent inhibitors of FMLP-and PAF-stimulated superoxide anion generation, beta-glucuronidase release (IC50 3-5 mumol/l) and Ca2+ influx while PGI2 and iloprost were ineffective at concentrations up to 10 mumol/l. These inhibitory actions of PGE1 and PGE2 were paralleled by an increase in cAMP level of the PMN while no change occurred with PGI2 and iloprost. None of the prostaglandins affected the initial intracellular Ca2+ liberation after challenge with FMLP or PAF. Preincubation of PMN with PGE1 and PGE2 but not with iloprost resulted in subsequent desensitization against a second administration of these compounds. None of the compounds affected PMN activation produced by arachidonic acid or calcimycin (A 23187). These data demonstrate that PGE-type compounds are effective inhibitors of receptor-mediated (PAF, FMLP) activation of human PMN while prostacyclins are considerably less potent. This suggests that the inhibitory prostaglandin receptor on human PMN belongs to the E-type being functionally different from the inhibitory prostaglandin receptor on human platelets. These results suggest that compounds, such as PGE1 and PGE2 might be superior to prostacyclins to prevent PMN-associated generation of reactive oxygen species and lysosomal enzyme release in situations with endogenous PMN activation, i.e. inflammatory reactions.

Physiological targets of superoxide anion and hydrogen peroxide in reperfusion injury.

Current dogma associates reperfusion injury with the introduction of reactive oxygen species (ROS) into the ischemic tissue. The sources of ROS under discussion are xanthine oxidase in the endothelium of small vessels and/or invaded polymorphonuclear leukocytes (PMN). The beneficial effects of both superoxide dismutase and catalase suggest an involvement of superoxide anions and hydrogen peroxide in this pathophysiological process, without describing the targets of their action. In our work we demonstrate that these two ROS effectively interact with two enzymes. Superoxide anions inhibit soluble guanylate cyclase. Its product, cGMP, is considered to antagonize platelet activation and to cause smooth muscle relaxation. Thus O2- can intensify platelet aggregability and small vessel occlusion. Similar effects are elicited by H2O2, which shifts the dose response curve of several agonists towards smaller concentrations by activating cyclooxygenase. This enzyme provides the substrate for thromboxane synthase which generates TxA2, the most potent physiologically occurring platelet aggregating and smooth muscle contacting agonist. These results lead us to the suggestion that the influence of the oxidative burst of PMN in the phenomenon of reperfusion injury should be reconsidered.

Potent inhibition of leukotriene (LT) B4 release from human polymorphonuclear leukocytes (PMN) by the PGE1-analogue OP-1206.

The present study investigates the inhibitory action of the PGE1-analogue OP-1206 on stimulated LTB4 release from human PMN. In comparison with PGE2, PGE1 and iloprost, OP-1206 was equipotent to PGE2 and PGE1 as inhibitor of PAF (3 microM) and FMLP (10 microM) induced LTB4 release even in the presence of exogenous arachidonic acid (10 microM). Iloprost was ineffective in this assay at a concentration of 10 microM. The data together with earlier observations suggest that E-type prostaglandins are potent inhibitors of receptor-mediated PMN activation and that these compounds may be valuable for prevention of PMN-associated tissue damage.