Effect of NO synthase inhibitor 2-amino-5,6-dihydro-4H-1,3-thiazine on endotoxin-induced changes in hemodynamic parameters and respiration in rats

Preclinical studies of NOS inhibitor T1059 vasopressor activity on the models of acute hemorrhagic shock in rats and dogs

The development of new effective and safe vasopressors is one of the ways to increase the effectiveness of the treatment of hypotensive disorders, the severe forms of which remain a common cause of death in all countries of the world. Previously, we synthesized the original compound T1059, a selective inhibitor of eNOS/iNOS which has a pronounced vasoconstrictive effect. Here we show its vasopressor activity in models of the early stage of acute hemorrhagic shock in rats and dogs, as part of preclinical studies. The results indicate NOS inhibitor T1059 as a potent long-acting vasopressor. Its single parenteral administration in sufficiently safe doses (1/50-1/9 LD10), caused in rats and dogs a rapid increase in vascular tone, accompanied by a prolonged hypertensive effect (within 90-120 min in rats, and within 115 min in dogs). The repeated administration of T1059 at low doses (1/3 of the first dose) made it possible to considerably (by at least 60 min) prolong a significant vasopressor effect. In all schemes, T1059 administration considerably inhibited the development of threatening cardiorespiratory disorders and significantly (p = 0.0026-0.0098) increased the short-term survival of experimental animals, formally extending the duration of the "golden hour" by 2 times. These data indicate that NOS inhibitors and, in particular, compound T1059, are able to create new opportunities in the treatment of hypotensive disorders, including the provision of assistance at the prehospital stage of treatment of such pathologies.

Radioprotective Activity of the Nitric Oxide Synthase Inhibitor T1023. Toxicological and Biochemical Properties, Cardiovascular and Radioprotective Effects

In this work, studies were performed to investigate the toxicological, biochemical, vasotropic and radiomodifying properties of the new nitric oxide synthase (NOS) inhibitor, compound T1023. Toxicological studies included the estimation of acute toxicity in mice after i.p. administration of T1023. Radiometric analysis and electron paramagnetic resonance spectroscopy were used to study NOS-inhibitory properties of T1023 in vitro and in vivo, respectively. T1023 vasoactive properties were studied in rat central hemodynamics. Radiobiological experiments were performed using endogenous and exogenous spleen colony formation as well as 30-day survival tests. The morphological changes in peripheral blood and bone marrow (BM) induced with T1023 were analyzed in mice during hematopoietic acute radiation syndrome (H-ARS). It was shown that T1023 is a sufficiently safe compound (LD10 of 317 mg/kg; LD50 of 410 mg/kg). It is an effective competitive NOS-inhibitor that is 10-to-15-fold selective to endothelial and inducible NOS (IC50 for nNOS, iNOS, eNOS: 52.3, 3.2 and 5.1 µM, respectively). Its NOS-inhibitory activity is realized in vivo and is accompanied by an increase in vascular tone. Its single i.p. administration in doses greater than 1/8 LD10 provides significant (40-50%) and long-lasting (more than 90 min) weakening of cardiac output, which can cause transient hypoxia. In radiobiological studies, T1023 proved to be a hypoxic radioprotector. Its radioprotective effect was observed only when administered prophylactically [single i.p dose, 5-120 min before total-body irradiation (TBI)] and only in doses that reduced cardiac output (1/8 LD10 and more, 40 mg/kg for mice), and was correlated in time with the dynamics of circulatory depression. Its radioprotective effect was not observed when administered in vitro and in the first 4 h after TBI. The optimal radioprotective doses of T1023 are relatively safe (1/ 5-1/4 LD10). In addition, T1023 effectively prevents H-ARS and gastrointestinal acute radiation syndrome (G-ARS) in experimental animals in vivo: dose modifying factor of 1.6-1.9. In the H-ARS mouse model, the prophylactic effect of T1023 (75 mg/kg, single i.p. injection) was accompanied by clinically significant effects. There was an express decrease in the degree of indicators of early BM devastation (by 40%) and maximal neutropenia and thrombocytopenia (2-2.5 times), in addition to a reduction in recovery time (by 30-40%). The obtained experimental results and literature data indicate that NOS inhibitors are an independent class of vasoactive radioprotectors with a specific hypoxic mechanism of action. NOS inhibitors provide new opportunities for developing effective and safe tools for the prevention of ARS.

Protective Effects of 2-Amino-5,6-dihydro-4H-1,3-thiazine and Its Derivative against Radiation-Induced Hematopoietic and Intestinal Injury in Mice

Ionizing radiation (IR) acts as an external stimulating factor, when it acts on the body, it will activate NF- κ B and cause the up-regulation of inducible nitric oxide synthase (iNOS) and induce a large amount of nitric oxide (NO) production. NO and other reactive nitrogen and oxygen species (RNS and ROS) can cause damage to biological molecules and affect their physiological functions. Our study investigated the protective role of 2-amino-5,6-dihydro-4H-1,3-thiazine hydrobromide (2-ADT) and 2-acetylamino-5,6-dihydro-4H-1,3-thiazine hydrobromide (2-AADT), two nitric oxide synthase inhibitors, against radiation-induced hematopoietic and intestinal injury in mice. Pretreatment with 2-ADT and 2-AADT improved the survival of mice exposed to a lethal dose of radiation, especially, the survival rate of the 2-ADT 20 mg/kg group was significantly higher than that of the vehicle group (p < 0.001). Our findings indicated that the radioprotective actions of 2-ADT and 2-AADT are achieved via accelerating hematopoietic system recovery, decreasing oxidative and nitrosative stress by enhancing the antioxidant defense system and reducing NO as well as peroxynitrite (ONOO − ) content, and mitigating the radiation-induced DNA damage evaluated by comet assay. These results suggest that 2-ADT and 2-AADT may have great application potential in ameliorating the damages of radiotherapy.