Mitogenic activity of selenoorganic compounds in human peripheral blood leukocytes

Prevention of nitrogen mustard-induced apoptosis in normal and transformed lymphocytes by ebselen

The alkylating agent, nitrogen mustard (HN2), is thought to cause apoptosis through production of free oxygen radicals. To explore the mechanism of HN2-induced apoptosis, we utilized ebselen, a selenoorganic compound with potent antioxidant activity. We examined whether ebselen would inhibit apoptosis in BALB/c mouse spleen lymphocytes and human MOLT-4 leukemia cells treated with HN2 (2.5 microM) in vitro. Non-toxic concentrations (<50 microM) of ebselen were found to prevent HN2-induced apoptosis of murine lymphocytes in a dose-dependent manner, as measured by cell viability, hypodiploid DNA formation, and phosphatidylserine externalization. However, ebselen was ineffective at preventing spontaneous apoptosis in these cells, pointing to the selectivity of its action. Furthermore, pretreatment with ebselen at 1-10 microM for 72 hr protected MOLT-4 cells from HN2-induced apoptosis and maintained cell viability and proliferation as monitored by the above-mentioned parameters. This was accompanied by the preservation of mitochondrial transmembrane potential and elevated glutathione levels and by a blockage of caspase-3 and -9 activation. In vivo, ebselen also had a marked protective effect against spleen weight loss associated with lymphocyte apoptosis in mice treated by HN2. Therefore, ebselen provides an efficient protection against HN2-induced cell death in normal and tumoral lymphocytes and might prove useful as an antidote against alkylating agents.

Modulation of cytokine production by a selenoorganic compound (AE-22) in hyperreactive or hyporeactive bronchoalveolar leukocytes of asthmatics or lung cancer patients

We have found that many synthetic selenoorganic compounds, including ebselen, have immunotropic activity. These studies were designed to assess the effect of the analog of ebselen bis[2-pyridyl (2-carbamoyl) phenyl]diselenide (AE-22) on human leukocytes that may express various activation states. The cells were obtained from bronchoalveolar lavage (BAL) cells of patients with various inflammatory lung diseases. The AE-22-treated BAL cells from patients with bronchial asthma (n = 6) and with small cell lung cancer (SCLC) (n = 6) were compared with these in the peripheral blood leukocytes (PBL) from the same donors. The control group comprised 5 patients who underwent diagnostic examination and were free of any cancer or concomitant diseases. Secretion of TNF-alpha, IL-6, and IFN-gamma was considered as a marker of BAL or PBL cell activation. Different response of the cells and various effects of AE-22 were observed in relation to the origin and functional state of leukocytes. It was established that AE-22 can induce TNF-alpha, IL-6, and IFN-gamma in a dose-dependent manner in BAL cells and PBL isolated from healthy individuals. However, BAL cells were found to be less reactive than PBL as cytokine producers. In contrast, AE-22 had no effect on BAL cells obtained from patients with lung cancer, which were found to be hyporeactive to phytohemagglutinin and bacterial lipopolysaccharide and did not produce TNF-alpha, IL-6, or IFN spontaneously. The spontaneous release of cytokines by BAL cells from bronchial asthma patients, but not by PBL from the same individuals, was significantly (p < 0.01) higher than that from the cultures of healthy control subjects. The high secretion of cytokines by the locally activated BAL cells was significantly (p < 0.01) reduced after administration of AE-22. The results suggest that AE-22 has immunomodulatory activity. AE-22 can downregulate the hyporeactive BAL cells from asthmatics, but it appears to be inactive in BAL cells of cancer patients who can tolerate the cytokine inducers.

Molecular actions of ebselen--an antiinflammatory antioxidant

1. Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) is a non-toxic seleno-organic drug with antiinflammatory, antiatherosclerotic and cytoprotective properties. 2. Ebselen and some of its metabolites are effective reductants of hydroperoxides including those arising in biomembranes and lipoproteins. 3. By reactions with hydroperoxides and thiols several interconversion cycles are formed which include ebselen metabolites with varying oxidation number of the selenium. 4. In the presence of thiols ebselen mimics the catalytic activities of phospholipid hydroperoxide glutathione peroxidase. 5. Ebselen inhibits at low concentrations a number of enzymes involved in inflammation such as lipoxygenases, NO synthases, NADPH, oxidase, protein kinase C and H+/K(+)-ATPase. The inhibitions are manifested on the cellular level and may contribute to the antiinflammatory potential of ebselen.

Ebselen, a selenoorganic compound as glutathione peroxidase mimic

The selenoorganic compound ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)-one, exhibits activity as an enzyme mimic. The reaction catalyzed is that of a glutathione (GSH) peroxidase (i.e., the reduction of a hydroperoxide at the expense of thiol). The specificity for substrates ranges from hydrogen peroxide and smaller organic hydroperoxides to membrane-bound phospholipid and cholesterol hydroperoxides. In addition to glutathione, the thiol reductant cosubstrate can be dithioerythritol, N-acetylcysteine or dihydrolipoate, or other suitable thiol compounds. Ebselen also has properties such as free radical and singlet oxygen quenching. Model experiments in vitro with liposomes, microsomes, isolated cells, and organs show that the protection against oxidative challenge afforded by ebselen can be explained largely by the activity as GSH peroxidase mimic. Whether this also explains the known preliminary results in clinical settings is yet open. The metabolism and disposition of ebselen is presented in this review. The main point is that the selenium is not bioavailable, explaining the extremely low toxicity observed in animal studies. The occurrence of natural GPx mimics, ovothiol and related compounds, is briefly mentioned.