[Radioprotective properties of isothiourea derivatives with NO-inhibitory mechanism of action].

The study of the radioprotective activity of S-[2-alkyl (aryl) sulfonyl]-S-ethyl derivatives of (vinyl)-isothiourea in (he model of the survival of mice exposed to gamma-radiation at a dose of 10 Gy has shown that the incorporation of additional sulfur-containing groups does not increase the radioprotective properties of compounds. In contrast to aminoalkil thiols, the effectiveness of the radiation protection action of the isothiourea (ITU) derivatives studied clearly correlates with the NO-inhibitory activity. This fact allowed us to assume that the radioprotective effect of S-substituted ITU caused inhibition of the endogenous synthesis of NO, which promotes the development of circulatory hypoxia, and that a further search for the radioprotective agents in this class of chemicals should be considered as the search for effective inhibitors of NO-synthase (NOS). The theoretical analysis of the conformity of molecular structures to the composition and topology of the active center of NOS-inhibitors allowed us to prognosticate a number of new ITU derivatives with the potential NOS-inhibiting ability. As a result of further theoretical and experimental studies, four S,N-disubstituted ITU derivatives - active non-selective NOS-inhibitors, were first identified and synthesized. These compounds exhibited a pronounced and prolonged vasopressive effects at doses of 0.01-0.05 LD50/15 in the models of severe hemorrhagic and endotoxic shock, and provided 65-100% 30-day survival at doses of 0.2-0.3 LD50/15 in the mice irradiated by gamma-rays at a dose of 10 Gy (LD98/30).The findings suggest the pronounced radioprotective effect of NOS-inhibitors among the ITU-derivatives.

Enhancement of antiradiation potential of some aminothiols by beta-carotene.

In the present study, protection of mice, BALB/c inbred as measured by survival at 30 days against whole-body gamma exposure at two dose levels, namely, 7.60 and 10.12 Gy by prior irradiation treatment with combination of beta-carotene, N-(2-mercapto-propionyl)-glycine (MPG) and S-(2-aminoethyl) isothiouroniumbromide hydrobromide (AET), is reported. It was found that administration of beta-carotene (1 mg per 20 g body mass) and 24 h before whole-body irradiation (7.60 Gy) had significantly improved the post-irradiation survival. It was also found that administration of a combination of AET (260 mg per kg body mass) and MPG (60 mg per kg body mass) 20 min before exposure to 7.60 Gy gamma irradiation to mice which have been treated with beta-carotene (1 mg per 20 g body mass) 24 h before exposure had resulted in 80% survival in comparison to 10% survival recorded for control animals. On the other hand, when the animals were exposed to a higher dose (10.12 Gy) under similar experimental conditions as above, a significant improvement in survival was observed during the first 10 days following the exposure but only a slight effect afterward. On the other hand, the response of male and female mice 10 days after exposure to the above radiation dose indicated that the females were more radioresistant than the males.

[Radioprotective agents in the decontamination of rats poisoned with percutaneously administered mustard gas]. / Dekontaminacija pacova perkutano trovanih S-iperitom pomocu radioprotektora.

The efficacy of rat skin decontamination by radioprotective agents AET and cystamine were tested. Results were compared to standard decontaminants-alcoholate, clay and fuller's earth. It was found that all the animals decontaminated with standard decontaminants had survived 4 LD50 of poison for 21 days. All the animals poisoned by 6 LD50 had survived for 1 day except for those decontaminated with alcoholate where 50% survived throughout the observation period. Alcoholate and clay protected all, and fuller's earth 70% of animals poisoned by 12 LD50, but no longer than 24 h. AET and cystamine protected all rats from 1.7 LD50 for 3 days, from 1 LD50 for 2 days, and from 2 LD50 for 1 day. When higher doses of poison were used (1.7-6.8 LD50) only partial protection was achieved. Our results support the conclusion that radioprotective agents could be convenient means for improvised decontamination of persons poisoned by sulfur mustard, so additional investigations are necessary.

Radioprotective efficacy of HT + AET in encapsulated form.

Entrapment of 5-hydroxyl-L-tryptophan (HT) in erythrocyte ghost prepared by hypotonic method and high voltage electric discharge method are nearly same. Release of HT with beta-aminoethylisothiuronium bromide hydrobromide (HT + AET) in in vitro system is rapid but only a portion of the entrapped amount is released. Release of HT + AET in serum marginally increases at 2 hr. Compared to release in in vitro medium the release in serum is less. Survival studies with Swiss albino mice indicates that compared to HT alone, the combination of HT + AET shows about 9 times percentage survival. The same combination in the encapsulated form show comparable percentage survival though the amount needed is 1/200th times compared to free form.

Radioprotective efficiency of a combination of hydroxytryptophan and AET on mouse bone marrow micronuclei.

Radioprotective effectiveness of a combination of HT and AET was evaluated by radiation induced micronucleus screening in mouse bone marrow. Swiss albino mice were injected with 2-Aminoethylisothiouronium bromide hydrobromide (AET)+5-hydroxy-L-tryptophan (HT) 30 minutes prior to a single whole body exposure of 8 and 12 Gy Co60 gamma rays. Animals were sacrificed at different intervals viz., 24 hours, 40 hours, 72 hours and 7 days after irradiation. Slides of femur marrow were screened thoroughly for cells with micronuclei. Marked decreases in the frequency of micronuclei in irradiated mice receiving radioprotector suggested that the combination has rendered protection to bone marrow cells against 8 Gy and 12 Gy whole body gamma irradiation. Micronucleated cells count is not altered by administration of the combination alone.

Use of hydroxylamine in improving radio protection of a combination of 5-hydroxy L-tryptophan and a thiol compound (AET) in small mammals.

Radioprotective effectiveness has been evaluated by 30 day survival studies and protection to bone-marrow cells in mice after radiation exposure and this has been further established by 24 hr deoxycytidine excretion in urine of rats following 5 Gy whole body gamma irradiation and protection to superoxide dismutase enzyme in marrow cells and red blood corpuscles. Radioprotective effectiveness as well as the duration of radioprotection have been improved by the administration (ip) of hydroxylamine (20 mg/kg), a decarboxylase inhibitor, prior to the use of a combination of 5-hydroxy L-tryptophan (5-HTP, 70 mg/kg) and 2-aminoethylisothiuronium bromide hydrobromide (AET, 20 mg/kg) ip in small mammals before whole body gamma irradiation.

Effect of some chemical radioprotectors on mouse bone marrow.

Effect of HT, AET and Se on mice bone marrow has been studied by counting bone marrow micronucleated cells and endogenous spleen colony count (CFU-S). Combination of HT and AET used as a radioprotector has not caused any significant variation in any of the parameter studied when administered once, it increases bone marrow micronucleated cells and decreases CFU-S slightly after daily administration for 7 days. The individual constituent of the combination administered singly does not increase micronucleated cell number. Seven consecutive doses of HT + AET and same in combination with Se enhances micronucleated cells to a higher level. Daily injection of Se alone up to 7 days also causes an increase in micronucleated cells upto same level. CFU-S pool does not show any significant change in number of bone marrow cells through out the study except in the groups where animals were treated with Se.

[Significance of ED50 and therapeutic indexes of various radiation-protective agent groups]. / Znacheniia ED50 i terapevticheskie indeksy razlichnykh grupp radioprotektorov.

Radioprotective agents are divided in 3 groups: (1) cystamine, AET, cystaphos, gammaphos, and thiogammaphos with ED50 (the dose that gives a half of the maximal protective effect) of 10(3)-10(1.6) mumol/kg and therapeutic index K = LD50/ED50 = 10(0)-10(1.6); (2) 5-methoxytryptamine, phenylephrine, serotonin, and norepinephrine with ED50 = 10(1)-10(0) mumol/kg and K = 10(1.8)-10(2,6); (3) clonidine and isoprenaline with ED50 = 10(-0.5)-10(-0.8) mumol/kg and K = 10(3)-10(4). Possible causes of these differences and advantages of low ED50 and high K are discussed.

Protection to glycolysis by a combination of 5-hydroxy-L-tryptophan and 2-aminoethylisothiuronium bromide hydrobromide in lethally irradiated rats.

Rate of glycolysis in vivo at different time intervals following 8 Gy [LD100(30)] whole body gamma radiation (WBGR) was evaluated by estimating liver glycogen, blood sugar, serum lactic dehydrogenase (LDH) and blood lactic acid concentration in adult male Sprague Dawley rats. Within 1 hr of radiation exposure, a significant fall in liver glycogen was observed in rats fed food and water ad libitum. The glycogen content increased after 24 hr and had returned to control level on 7th day after radiation exposure. Blood sugar, serum LDH and blood lactate levels increased significantly as compared to non irradiated controls. Pretreatment with 5-hydroxy-L-tryptophan (5-HTP; 100 mg/kg) + 2-aminoethylisothiuronium bromide hydrobromide (AET; 20 mg/kg) ip 30 min before 8 Gy WBGR, modified these values and restored them to normal level on 7th day post-irradiation.

Radioprotection of spleen by a combination of 5-hydroxy-L-tryptophan and 2-aminoethylisothiuronium bromide hydrobromide in lethally irradiated rats.

Radioprotective efficiency of the combination of 5-hydroxy-L-tryptophan (5-HTP, 100 mg/kg) with 2-aminoethylisothiuronium bromide hydrobromide (AET, 20 mg/kg) in protecting splenic tissue following 8 Gy whole-body gamma radiation (WBGR) has been studied in adult male Sprague Dawley rats. Loss in splenic weight, splenic cells and DNA was observed following & Gy WBGR, which was modified significantly in 5-HTP+AET (ip) pretreated group. The study further showed that pre-treatment with this formulation led to an increased superoxide dismutase (SOD) activity and a decrease in lactate/pyruvate ratio in the cytosol fraction of the spleen.

Effects of AET and MEA on the lysosomal hydrolase activities in the mouse organs.

The adult male Swiss mice were injected intraperitoneally with AET (2-aminoethylisothiouronium Br.HBr) or MEA (cysteamine HCl), in a toxic dose of 400 mg/kg body weight. The acid phosphatase (E.C. 3.1.3.2) and arylsulphatase (E. C. 3.1.6.1) activities in crude homogenates of liver and kidneys were assessed every fourth hour throughout a 24-h period. Different patterns of temporal changes in the acid phosphatase and arylsulphatase activities in liver and kidneys expressed in nkat per 1 mg of protein, 1 g of fresh tissue and per the whole organ weight, were found. The extent and timing of the alterations in the activity of each of the lysosomal hydrolases were dependent on the particular organ chosen and aminothiol compound given.

[Radiation injuries to mice in relation to the modes of administration of adeturon]. / Radiatsionnoe porazhenie myshei v zavisimosti ot sposobov primeneniia adeturona.

In experiments with mice the influence of adeturon, a preparation obtained in Bulgaria, on the survival rate, leucocytes dynamics, cellularity of bone marrow and spleen, and on nucleic acids in the peripheral blood has been investigated. The comparative analysis of the results obtained indicates that the protective and therapeutic administration of adeturon is more effective than a single injection of the drug immediately after irradiation.

Influence of mixed-ligand complexes on retention and distribution of radioniobium in mice.

The individual effects of desferrioxamine B (DFOA), Na3Ca diethylenetriaminepentaacetic acid (DTPA), Na-salicylate, DL-penicillamine, and 2-aminoethylisothiouronium bromide hydrobromide, as well as the effect of mixed-ligand treatment on the retention and elimination of 95Nb in mice have been examined. It was found that 95Nb could easily be mobilized by a single dose of DFOA, but the best result was obtained with the DFOA and DTPA combination. Mixed-ligand treatment did not change the deposition characteristics and translocation kinetics of 95Nb.

Antimutagenic properties of WR 2721 and of a radioprotective mixture, ATP-AET-serotonin, with regard to X ray induced reciprocal translocations in mouse spermatogonia.

Pretreatment by intraperitoneal administration of WR 2721 at 400 mg/kg body weight in mice receiving 4.0 Gy X rays was found to have an appreciable antimutagenic effect with regard to reciprocal translocation induction in spermatogonia. The effectiveness of the product tested proved superior to that of a radioprotective mixture of ATP-AET-serotonin given at optimal dose ratio--360, 24, and 8 mg/kg body weight, respectively. The RF (Reduction Factor) was 2.4 for WR 2721 and 1.8 for the mixture. The effect observed indicated WR 2721 to have potential capabilities for reducing the genetic risk of radiation in male individuals.

Life span and tumor incidence in rats receiving postradiation treatment with ATP-AET-mexamine mixture.

Rat females were exposed to a single 4.0-Gy gamma-ray dose and treated postradiation with a mixture of ATP-AET-mexamine at daily doses of 24, 12, and 3 mg/kg body wt, respectively, in drinking water throughout the period of their survival. With the radiation dose used, life shortening appeared primarily attributable to nonstochastic effects. The mixture of chemical protectors failed to show modification of long-term radiation effects with regard to either life span or tumor incidence.

Protection with combinations of hydroxytryptophan and some thiol compounds against whole-body gamma irradiation.

Protection of mice (as measured by survival at 30 days) against whole-body gamma exposure by prior treatment with combinations of hydroxytryptophan (HT) and some thiol drugs, is reported here. The combination of HT and aminoethylisothiuronium bromide hydrobromide (AET) was much more effective than HT alone against the effects of 10.5 and 12.5 Gy of gamma ray exposure. A combination of HT and beta-mercaptopropionylglycine (MPG) gave marked protection against a 10.5 Gy exposure but not against 12.5 Gy. The combination of HT with cysteine or cysteamine also provided reasonable protection against 10.5 Gy. The combination of HT and cystamine rendered a low level of protection against 10.5 Gy, but again it was better than HT alone. The thiol drugs by themselves in the doses used in combination were ineffective in rendering protection after whole body gamma ray exposure.