Differential activity of NO synthase inhibitors as chemopreventive agents in a primary rat tracheal epithelial cell transformation system. (1/19)

A model to study the effectiveness of potential chemopreventive agents that inhibit neoplastic process by different mechanisms has been used to test the efficacy of seven nitric oxide synthase (NOS) inhibitors. Five selective inducible NOS (iNOS) inhibitors: S-methyl isothiourea (S-MITU), S-2-aminoethyl isothiourea (S-2-AEITU), S-ethyl isothiourea (S-EITU), aminoguanidine (AG), 2-amino-4-methyl pyridine (2-AMP), and two non selective general NOS inhibitors: l-N(6)-(1-iminoethyl) lysine (IEL) and N(omega)-nitro-l-arginine (NNLA), were tested for efficacy against a carcinogen, benzo[a]pyrene (B[a]P)-induced primary rat tracheal epithelial (RTE) cell transformation assay. RTE cells were treated with B[a]P alone or with five nontoxic concentrations of an NOS inhibitor and the resulting foci at the end of 30 days were scored for inhibition of transformation. The results indicate that all three isothiourea compounds inhibited B[a]P-induced RTE foci in a dose-dependent manner. S-AEITU was the most effective inhibitor with an IC(50) (the molar concentration that inhibits transformation by 50%) of 9.1 microM and 100% inhibition at the highest dose tested (30 microM). However, both S-EITU and S-MITU showed a maximum percent inhibition of 81% and 100% at 1 mM with an IC(50) of 84 and 110 microM, respectively. 2-AMP did not show any dose-dependent response, but was highly effective (57% inhibition) at an intermediate dose of 30 microM and an IC(50) of 25 microM. Similar to thiourea compounds, AG exhibited good dose-dependent inhibition with a maximum inhibition of 86% at 1 mM. NNLA and IEL were negative in this assay. Based on the IC(50) values, NOS inhibitors were rated for efficacy from high to low as follows: S-2-AEITU<2-AMP+info)

A case of small-cell Sezary's syndrome with null-cell features. (2/19)

A case of the small-cell variant of Sezary's syndrome (SS) is reported in which the SS cells lacked the surface-marker characteristics of both T- and B-cells. In particular, the SS cells failed to form E-rosettes even with a sensitive technique using 2-amino-ethylisothiouronium bromide (AET)-treated sheep red blood cells. The significance of these findings is briefly considered in relation to the existing literature.  (+info)

Induction of the paroxysmal nocturnal hemoglobinuria phenotype in normal human erythrocytes: effects of 2-aminoethylisothiouronium bromide on membrane proteins that regulate complement. (3/19)

To investigate the mechanism by which treatment of normal human erythrocytes with the sulfhydryl reagent 2-aminoethylisothiouronium bromide (AET) induces susceptibility to complement mediated lysis, the effects of AET on the structural and functional integrity of decay accelerating factor (DAF), membrane inhibitor of reactive lysis (MIRL), and complement receptor type 1 (CR1) were examined. Following treatment with AET, erythrocyte MIRL and CR1 were no longer recognized in situ by antibodies, and antibody binding to DAF was diminished by approximately 50%. These studies indicated that the structural integrity of the three complement regulatory proteins was either partially (DAF) or completely (MIRL and CR1) disrupted by AET. Subsequent experiments showed that functional inactivation paralleled the structural disruption. Treatment of normal erythrocytes with AET induced susceptibility to cobra venom factor-initiated hemolysis, indicating that the functional activity of MIRL had been destroyed. The capacity of erythrocyte CR1 to serve as a cofactor for factor I-mediated cleavage of iC3b to C3c and C3dg was lost following treatment with AET. C3 convertase activity increase markedly following treatment of erythrocytes with AET, but convertase activity on AET cells was approximately 50% less than that observed when DAF function on normal cells was completely inhibited by antibody. Susceptibility of AET cells to acidified serum lysis was shown to be due primarily to inactivation of MIRL. Unexpectedly, in acidified serum the activity of the amplification C3 convertase of the APC was found to be controlled by MIRL as well as by DAF. These studies show that AET induces susceptibility to complement-mediated lysis by disrupting the structural and functional integrity of membrane constituents that regulate the activity of both the C3 convertases and the membrane attack complex of complement.  (+info)

The role of nitric oxide in radiation damage. (4/19)

This study investigated the role of nitric oxide in radiation-induced damage by examining changes in mouse serum nitrate concentrations after irradiation. In addition, the contribution of S-2-aminoethylisothiourea 2HBr (AET) to the mechanisms of radiation damage protection was also clarified. The serum nitrate concentration increased as soon as 1.5 h after irradiation, and after 2.5 to 3.0 h the concentrations were significantly higher compared with normal levels. Normal levels were re-established after 12 h. Post-irradiation serum nitrate concentrations increased dose-dependently with irradiation dose (19.6-31.5 Gy). AET suppressed increases in the serum nitrate concentration following irradiation while 2-mercaptoethylamine HCl (MEA) did not. AET has an inhibitory effect on inducible nitric oxide synthase (iNOS); therefore, the increase in nitric oxide after irradiation may be produced by iNOS. Combined administration of irradiation and lipopolysaccharide (LPS) induced a significant increase in serum nitrate concentration, and a significant decrease in survival rate, compared with irradiation alone. The administration of AET or aminoguanidine increased survival rate following irradiation. In contrast to findings after LPS administration, IL-1beta and IFN-gamma were not determined in serum following irradiation. Existing iNOS is activated by irradiation, and nitric oxide production appears to increase without iNOS induction. Thus, the irradiation-induced increase in nitric oxide may be related to lethal injury.  (+info)

Immunoblotting human C4 bound to human erythrocytes in vivo and in vitro. (5/19)

A study of C4 bound to human erythrocytes in vitro and in vivo has been made by immunoblotting with mouse monoclonal anti-C4c and anti-C4d and human polyclonal anti-C4d (Rodgers and Chido) following SDS-PAGE. Multi-banded patterns differentiated between C4A and C4B isotypes. Treatment of EC4b with trypsin eliminated immunoblotting but not agglutination reactions. Serum inactivation (factor I) of EC4b resulted in banding patterns similar to those obtained from patients' EC4d. Treatment of EC4b membranes with NH2OH affected many of the bands, two were lost, one was markedly reduced and others had altered SDS-PAGE mobility. Interpretation of the bands has been made in terms of C4-acceptor complexes and inactivation fragments of C4. A distinct difference in the banding of C4A and C4B isotypes has been detected.  (+info)

Tumor rejection in experimental animals treated with radioprotective thiols. (6/19)

In experimental animals, a systemic treatment with thiols of the mercaptoalkylamine type has affected all of five solid tumors so far investigated. (Three of the tumors were transplanted into the strain of origin.) There was either inhibition of growth or "oncodieresis," i.e., a necrosis and sloughing of tumors conducive to full recovery and repair. Mercaptoalkylamines and derivatives of the type used in our experiments are known to bind to cellular sites by a two-point attachment involving both thiol and amino groups. One of these compounds, cysteamine, was active in its native, unsubstituted form, but did not bring about oncodieresis when either the amino or thiol group, or both, were alkylated. Mercaptopropylamine, the 3-carbon homolog of cysteamine, was less active. Cystamine, a disulfide dimer of cysteamine that has no free reactive sulfhydryl, did not induce any reaction. Thioglycerol, lacking a terminal amino group, had only negligible activity. Rejection was much more striking when treatment was started on the day of inoculation than when started 7 days later. Male mice rejected better than females. Results were inferior when tow of the agents were given simultaneously or together with other radioprotectants, such as L-cysteine, glutathione, dimethyl sulfoxide, or reserpine. Tumor rejection was enhanced when the phosphorylated thioyls, S-2-(3-aminopropylamino)ethylphosphorothioic acid or S-(2-ethylguanidine)phosphorothioci acid, were given simultaneously with the radioprotective serotonin, but there was no synergy of serotonin with the nonphosphorylated compounds S-2-aminoethylisothiouronium bromide or cysteamine. Serotonin alone did not affect the tumors.  (+info)

Characterization of the complement sensitivity of paroxysmal nocturnal hemoglobinuria erythrocytes. (7/19)

The affected erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH II and PNH III cells) are abnormally sensitive to complement-mediated lysis. Normal human erythrocytes chemically modified by treatment with 2-amino-ethylisothiouronium bromide (AET) have been used as models for PNH cells inasmuch as they also exhibit an enhanced susceptibility to complement. To investigate the bases for the greater sensitivity of these abnormal cells to complement-mediated lysis, we compared binding of C3 and constituents of the membrane attack complex to normal, PNH II, PNH III, and AET-treated cells after classical pathway activation by antibody and fluid-phase activation by cobra venom factor complexes. When whole serum complement was activated by antibody, there was increased binding of C3 and C9 to PNH II, PNH III, and AET-treated cells, although the binding of these complement components to PNH II and PNH III cells was considerably greater than their binding to the AET-treated cells. In addition, all of the abnormal cell types showed a greater degree of lysis per C9 bound than did the normal erythrocytes. PNH III and AET-treated cells were readily lysed by fluid-phase activation of complement, whereas normal and PNH II erythrocytes were not susceptible to bystander lysis. The greater hemolysis of PNH III and AET-treated cells in this reactive lysis system was due to a quantitative increase in binding of constituents of the membrane attack complex. This more efficient binding of the terminal components after fluid-phase activation of whole serum complement was not mediated by cell-bound C3 fragments. These investigations demonstrate that the molecular events that characterize the enhanced susceptibility of PNH II, PNH III, and AET-treated erythrocytes to complement-mediated lysis are heterogeneous.  (+info)

Tissue NAD levels and the response to irradiation of cytotoxic drugs. (8/19)

It has been shown that when (32)P counting from a tumour is continuous peaks in the count rate can sometimes be induced by large doses of nicotinic acid, nicotinic acid, nicotinamide or 3-acetylpyridine, but not by 6-aminonicotinamide. These (32)P counting peaks have been associated with the time of maximal new synthesis of nicotinamide adenine dinucleotide (NAD). Sensitization to irradiation or some cytotoxic drugs has been found at the peak of this new NAD synthesis. The radioprotective agents cysteamine, 2-aminoethylisothiouronium bromide (AET) and serotonin have been found to cause a rapid fall in tissue NAD levels. The results have been briefly discussed.  (+info)

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