Selenium pretreatment enhances the radioprotective effect and reduces the lethal toxicity of WR-2721

Although WR-2721, S-2-(3-aminopropylamino)ethylphosphorothioic acid, is an effective radioprotector, its use is limited by its toxicity. Combining WR-2721 with other agents might decrease its toxicity and/or increase its effectiveness. The effect of selenium (Se) pretreatment on the acute toxicity and radioprotective effect of WR-2721 was studied in male CD2F1 mice. Injection of 1.6 mg/kg Se 24 hr before WR-2721 (800-1200 mg/kg, IP) decreased the lethality of WR-2721 significantly. Lower doses of Se were also effective, but simultaneous administration was not effective. Se injection alone (1.6 mg/kg) 24 hr before cobalt-60 irradiation increased the survival (dose reduction factor, DRF = 1.1) significantly. A synergistic effect on post-irradiation survival was observed when Se was injected 24 hr before WR-2721 (200-600 mg/kg IP 1/2 before irradiation). For example, after exposure to 22 Gy (1 Gy/min), 30-day survival was 100% when mice were treated with both Se and 600 mg/kg WR-2721, and was 13% with WR-2721 alone. The DRF after 400 mg/kg WR-2721 was 2.6 with Se compared to 2.2 without Se pretreatment. Alkaline phosphatase activity in bone marrow cells and serum was significantly depressed after treatment with 1.6 mg/kg Se, suggesting that a retardation of conversion of WR-2721 to its active free sulfhydryl form through the action of alkaline phosphatase might be partly responsible for the effects of Se. Other possible mechanisms related to the antioxidant properties of Se are under investigation.

Inhibition of glutathione peroxidase and glutathione transferase in mouse liver by misonidazole

The mechanisms of toxicity and sensitization by the radiosensitizer misonidazole [1-(2-nitro-1-imidazolyl)-3-methoxy-2-propanol] are not well understood. We report here on the inhibition of total glutathione peroxidase (GSHPx), selenium-dependent glutathione peroxidase (selenium-GSHPx) and glutathione transferase (GSHTx) activities by misonidazole. Mouse liver cytosol GSHPx and selenium-GSHPx were inhibited in vitro with 0.5 mM misonidazole. On administration of the drug intraperitoneally (800 mg/kg) to mice, it was found that GSHPx, selenium-GSHPx, and GSHTx were inhibited in homogenate, cytosol, and microsomal fractions of mouse liver. GSHPx was depressed in all fractions up to 60-70% of control values, with maximum depression occurring in the cytosol and homogenate fractions in less than 2 hr. Recovery of activity was slower in the microsomes. In general, the pattern of depression of selenium-GSHPx was parallel to that of GSHPx except in microsomes, where GSHPx is minimal. Quantitatively, selenium-GSHPx was least affected. GSHTx was inhibited 70-80% of control values in cytosol and homogenate with recovery by 24 hr, whereas a second period of depression occurred at 24 hr in the microsomes. The inhibition of peroxide-metabolizing enzymes may lead to elevation of intracellular peroxide levels, contributing to the radiosensitizing effect and/or toxicity of misonidazole.

A novel interaction of diethyldithiocarbamate with the glutathione/glutathione peroxidase system

Diethyldithiocarbamate (DDC) exhibits a variety of pharmacologic activities, including both radioprotective and sensitizing properties. Since the glutathione/glutathione peroxidase system may be a significant factor in determining radiation sensitivity, the potential mechanisms of action of DDC in relation to this system were examined in vitro. The interaction of DDC with reduced glutathione (GSH) was tested using a simple system based on the reduction of cytochrome c. When DDC (0.005 mM) was incubated with GSH (0.5 mM), the reduction of cytochrome c was eightfold greater than that expected from an additive effect of DDC and GSH. GSH could be replaced by oxidized glutathione and glutathione reductase. Cytochrome c reduced by DDC was oxidized by mitochondria. The interaction of DDC with both the hexosemonophosphate shunt pathway and the mitochondrial respiratory chain suggests the possibility of linking these two pathways through DDC. Oxidation of DDC by peroxide and reversal by GSH indicated that the drug can engage in a cyclic reaction with peroxide and GSH. This was confirmed when DDC was used in the assay system for glutathione peroxidase (GSHPx) without GSHPx. DDC at a concentration of 0.25 mM was more active than 0.01 unit of pure GSHPx in eliminating peroxide, and much more active than the other sulfhydryl compounds tested. These studies indicate that DDC can supplement GSHPx activity or substitute for it in detoxifying peroxides, and suggests a unique role in the chemical modification of radiation sensitivity.

Agranulocytosis associated with chronic oral administration of cloxacillin for suppression of staphylococcal osteomyelitis

Oral cloxacillin was used for chronic suppression of a 59-year-old woman with staphylococcal osteomyelitis. She received 380.5 gm of cloxacillin over 263 consecutive days. Severe agranulocytosis followed, reverting rapidly to normal with cessation of drug. The absence of signs of an allergic reactions such as rash, fever, or eosinophilia suggests that cloxacillin, like other semisynthetic penicillins, may exert a direct bone marrow toxicity.

Impaired antibody responses to a pneumococcal polysaccharide vaccine in patients with non-Hodgkin's lymphoma in remission

Eight patients with non-Hodgkin's lymphoma who have been in complete clinical remission for the mean of 23.3 months were evaluated for their antibody responses to a pneumococcal vaccine. The results were correlated with lymphocyte subpopulations, serum immunoglobulin levels, and in vitro mitogenic responses to phytohemagglutinin, concanavalin and pokeweed mitogen. Two patients with normal antibody responses had immunoglobulin levels and mitogenesis within the range of controls. Impaired antibody responses in the remaining six patients were correlated either with marked depressed mitogenesis to phytohemagglutinin or with low levels of IgA. Impaired humoral immune responses seem to persist in these patients even after several months of sustained clinical remission.

Hemolytic anemia in Wilson disease: clinical findings and biochemical mechanisms

Two patients with Wilson disease who presented with severe hemolytic anemia are described. One was noted to have unusually high serum copper levels (369 micrograms/100 ml). A review of similar such patients in the literature suggests that, rather than having a low serum copper, patients with hemolysis accompanying Wilson disease have very high serum copper levels. For this reason, in vitro studies of the toxic effects of copper on erythrocytes were undertaken. It was found that, although copper does not have a major direct inhibitory effect on glycolytic enzymes such as hexokinase, the metal does inhibit hexokinase as a consequence of its interaction with oxyhemoglobin. However, such inhibition does not appear to be a major factor in copper-induced hemolysis. On the other hand, the addition of the lipid antioxidant butylated hydroxyanisole (BHA) suppresses hemolysis in copper-treated cells. These experiments suggest that the primary toxic effect of copper is mediated through its oxidant actions on membrane phospholipids rather than through its potential inhibitory effects on intracellular enzymes.

Levamisole inhibition of microsomal lipid peroxidation as related to its sulfhydryl metabolite dl-2-oxo-3-(2-mercaptoethyl)-5-phenylimadazolidine

Levamisole was previously shown to protect rat liver microsomes from lipid peroxidation induced by ADP-Fe and either NADPH, ascorbate, or X irradiation. The present experiments provide information about the mechanism of protection. Incubation of levamisole with a microsomal system containing ADP-Fe and NADPH resulted in protection of sulfhydryl groups, whereas reaction of levamisole with ascorbate (nonenzymatic system) indicated generation of a sulfhydryl metabolite. Production of a sulfhydryl metabolite of levamisole, dl-2-oxo-3-(2-mercaptoethyl)-5-phenylimidazolidine (OMPI), in either the enzymatic or nonenzymatic system was demonstrated by gas chromatography-mass spectrometry. While levamisole acts as an antioxidant at concentrations of 1.0 and 2.0 mM, OMPI had an enigmatic effect on microsomal lipid peroxidation induced enzymatically or nonenzymatically. OMPI exhibited a biphasic effect: at concentrations below 25 microM a prooxidant effect was observed, and at concentrations exceeding 50 microM an antioxidant effect was observed. The data suggest that the inhibition of microsomal lipid peroxidation by levamisole is due to the generation of a sulfhydryl metabolite and that the active intermediate is probably OMPI.

Induction of guanine deaminase and its inhibitor in rodent liver and brain

1. Guanine deaminase activities in homogenates and supernatant fractions of liver and brain of rat and mouse were elevated by administration of guanine to the animals. The maximum induction in mouse tissues occurred within 24h and in rat tissues within 48h. 2. Mitochondria of rat (but not mouse) liver and brain contain an inhibitor of supernatant guanine deaminase, and this was also increased by guanine treatment. 3. Administration of ethionine, cycloheximide or actinomycin D prevented the guanine-dependent increase in deaminase activity and also the increase in mitochondrial inhibitory activity; chloramphenicol suppressed only the latter.

Guanine deaminase inhibitor from rat liver. Isolation and characterization

1. An inhibitor of cytoplasmic guanine deaminase of rat liver was isolated from liver ;heavy mitochondrial' fraction after freezing and thawing and treatment with Triton X-100. 2. Submitochondrial fractionation revealed that the inhibitor was localized in the outer-membrane fraction. 3. The method of purification of inhibitor, involving precipitation with (NH(4))(2)SO(4) and chromatography on DEAE-cellulose, its precipitability by trichloroacetic acid and the pattern of absorption in the u.v. indicated that the inhibitor was a protein. In confirmation, tryptic digestion of the isolated material resulted in destruction of the inhibitor activity. The inhibitor was stable to acid, but labile to heat. 4. The isolated inhibitor required phosphatidylcholine (lecithin) for activity. Phosphatidylcholine also partially protected the inhibitor against heat inactivation. 5. When detergent treatment was omitted, the inhibitor activity of frozen mitochondria was precipitated by (NH(4))(2)SO(4) in a fully active form without supplementation with phosphatidylcholine, indicating that Triton X-100 ruptured the linkage between inhibitor and lipid. 6. A reconstituted sample of inhibitor-phosphatidylcholine complex was precipitated in a fully active form by dialysis against 2-mercaptoethanol, but treatment of the precipitate with NaCl yielded an extract which was inactive unless supplemented with fresh phosphatidylcholine. 7. We interpret the results as evidence that the inhibitor was present in vivo as a lipoprotein and that once the complex was dissociated by the action of detergent and the protein precipitated, there was an absolute need for exogenous phosphatidylcholine for its activity. The manner in which inhibitor associated with the outer membrane of rat liver mitochondria might regulate the activity of the enzyme in the supernatant has been suggested.

Modulation of guanine deaminase

1. Guanine deaminases purified from the 15000g supernatant fraction of iso-osmotic sucrose homogenates of rat and mouse liver and brain were tested for the influence of GTP and allantoin. 2. The suffixes A and B were assigned to the isoenzyme fractions eluted from DEAE-cellulose with the lower and the higher molarity of eluent respectively. Isoenzyme A from rat liver, the activity of which showed a sigmoid dependence on substrate saturation, was activated by GTP and inhibited by allantoin. Isoenzyme B, which had a hyperbolic substrate-saturation curve, was not influenced by GTP or allantoin. 3. Isoenzyme A from rat brain, the activity of which had a sigmoid dependence on substrate concentration, was stimulated by GTP. Isoenzyme B, which showed classical Michaelis-Menten kinetics, was inhibited by allantoin. 4. Mouse liver guanine deaminase was not influenced by either GTP or allantoin. 5. Isoenzyme A from mouse brain, which had a hyperbolic substrate-saturation curve, was not influenced by GTP or allantoin but isoenzyme B, with sigmoidal kinetics, was inhibited by allantoin. 6. Mg(2+) activated, or inhibited or did not have an effect on guanine deaminase, depending on the source of the enzyme. 7. The bearing of the above findings on the possible regulation of guanine deaminase activity in vivo is discussed.

Guanine deaminase in rat liver and mouse liver and brain

1. The guanine deaminase in rat liver supernatant preparations was resolved into two fractions, A and B, on DEAE-cellulose columns. The two differed in electrophoretic mobility and in various properties. The most noteworthy distinction between A and B components was that the enzyme A activity showed a sigmoid dependence on substrate concentration whereas the enzyme B showed classical Michaelis-Menten kinetics. The K(m) value of enzyme A for guanine was 5.3mum and that of enzyme B 20mum. 2. The entire guanine deaminase activity of mouse liver was contained in the 15000g supernatant of iso-osmotic homogenates. 3. A reinvestigation of the behaviour of rat brain 15000g supernatant guanine deaminase isoenzymes revealed that one enzyme had sigmoidal kinetics and the other enzyme showed a hyperbolic response. 4. Of the guanine deaminase in mouse brain iso-osmotic sucrose homogenate 80% was recovered in the 15000g supernatant and the rest from the particles. The supernatant guanine deaminase was resolvable into two fractions on DEAE-cellulose columns. One enzyme showed sigmoidal kinetics whereas the other showed a hyperbolic response to increasing substrate concentration; the K(m) values for the reaction with guanine were respectively 5 and 66mum. 5. The particulate fractions of mouse liver and brain were devoid of any overt inhibitory activity.

Delayed effects of S-beta-aminoethylisothiouronium bromide hydrobromide (AET) administration on lipid metabolism

Various doses of S-β-aminoethylisothiouronium bromide hydrobromide (AET), one of the most promising radioprotectors to date, were administered to rats by a single intraperitoneal injection. Doses of up to 200 mg/kg body weight were tolerated but doses of 250 mg/kg body weight and above were toxic. There was accumulation of lipids in liver of rats 30 days after AET administration. Acetate-1-14C incorporation into total lipids, fatty acids, and nonsaponifiable lipids of liver, kidney, and spleen was inhibited by AET administration.