(S)-Methylisothiourea sulfate

Beneficial effects and improved survival in rodent models of septic shock with S-methylisothiourea sulfate, a potent and selective inhibitor of inducible nitric oxide synthase.[Pubmed:7528923]

Proc Natl Acad Sci U S A. 1994 Dec 20;91(26):12472-6.

Enhanced formation of nitric oxide (NO) by both the constitutive and the inducible isoforms of NO synthase (NOS) has been implicated in the pathophysiology of a variety of diseases, including circulatory shock. Non-isoform-selective inhibition of NO formation, however, may lead to side effects by inhibiting the constitutive isoform of NOS and, thus, the various physiological actions of NO. S-Methylisothiourea sulfate (SMT) is at least 10- to 30-fold more potent as an inhibitor of inducible NOS (iNOS) in immunostimulated cultured macrophages (EC50, 6 microM) and vascular smooth muscle cells (EC50, 2 microM) than NG-methyl-L-arginine (MeArg) or any other NOS inhibitor yet known. The effect of SMT on iNOS activity can be reversed by excess L-arginine in a concentration-dependent manner. SMT (up to 1 mM) does not inhibit the activity of xanthine oxidase, diaphorase, lactate dehydrogenase, monoamine oxidase, catalase, cytochrome P450, or superoxide dismutase. SMT is equipotent with MeArg in inhibiting the endothelial, constitutive isoform of NOS in vitro and causes increases in blood pressure similar to those produced by MeArg in normal rats. SMT, however, dose-dependently reverses (0.01-3 mg/kg) the hypotension and the vascular hyporeactivity to vasoconstrictor agents caused by endotoxin [bacterial lipopolysaccharide (LPS), 10 mg/kg, i.v.] in anesthetized rats. Moreover, therapeutic administration of SMT (5 mg/kg, i.p., given 2 hr after LPS, 10 mg/kg, i.p.) attenuates the rises in plasma alanine and aspartate aminotransferases, bilirubin, and creatinine and also prevents hypocalcaemia when measured 6 hr after administration of LPS. SMT (1 mg/kg, i.p.) improves 24-hr survival of mice treated with a high dose of LPS (60 mg/kg, i.p.). Thus, SMT is a potent and selective inhibitor of iNOS and exerts beneficial effects in rodent models of septic shock. SMT, therefore, may have considerable value in the therapy of circulatory shock of various etiologies and other pathophysiological conditions associated with induction of iNOS.

S-Methylisothiourea sulfate improves renal, but not hepatic dysfunction in canine endotoxic shock model.[Pubmed:10663292]

Intensive Care Med. 2000 Jan;26(1):117-24.

OBJECTIVE: Excess production of nitric oxide (NO) by inducible NO synthase (iNOS) has been implicated in the pathophysiology of septic shock. This study was designed to see whether S-methylisothiourea sulfate (SMT), a selective inhibitor for iNOS, prevents cardiovascular changes and multiple organ damage in the canine endotoxic shock model. DESIGN: Prospective, comparable, experimental study. SETTING: Laboratory at a university hospital. SUBJECTS: Twenty male mongrel dogs were studied under pentobarbital anesthesia. INTERVENTIONS: Dogs were divided into three groups: bacterial lipopolysaccharide (LPS) group (n = 7) receiving continuous infusion of LPS (2 mg/kg/h for 1 h); LPS plus SMT group (n = 7) receiving LPS and SMT (1 mg/kg, bolus i. v., followed by continuous infusion of 1 mg/kg/h for 1 h); and vehicle plus SMT group (n = 6). MEASUREMENTS AND RESULTS: Hemodynamics, blood gas parameters, and urine output were measured during 6 h observation periods. Serum levels of lactate, transaminases, and bilirubin were measured at baseline, 1 and 6 h. Creatinine and free water clearance, urine sodium excretion and fractional excretion of sodium were calculated. LPS caused a profound hypotension associated with decreases in cardiac output and oxygen delivery, lactic acidosis, renal and liver dysfunction, and thrombocytopenia. SMT prevented the LPS-induced hypotension and renal dysfunction, whereas it did not affect the LPS-induced decreases in cardiac output or oxygen delivery, hyperlactatemia, liver dysfunction, or thrombocytopenia. SMT alone had no appreciable effects on hemodynamics, blood gases, liver or renal functions. CONCLUSIONS: These findings show that SMT improves renal, but not hepatic dysfunction, in dogs with endotoxic shock, suggesting that iNOS-derived NO plays differential roles in sepsis-associated multiple organ dysfunction.

Protective effects of S-methylisothiourea sulfate on different aspiration materials-induced lung injury in rats.[Pubmed:18573544]

Int J Pediatr Otorhinolaryngol. 2008 Aug;72(8):1241-50.

OBJECTIVES: The aim of this study was to evaluate the efficiency of inducible nitric oxide synthase (iNOS) specific inhibitor, S-methylisothiourea sulfate (SMT) in preventing lung injury after different pulmonary aspiration materials in rats. MATERIAL AND METHODS: The experiments were performed in 80 Sprague-Dawley rats, ranging in weight from 220 to 250 g, randomly allotted into one of the eight groups (n=10): normal saline (NS, control), Biosorb Energy Plus (BIO), sucralfate (SUC), hydrochloric acid (HCl), NS+SMT treated, BIO+SMT treated, SUC+SMT treated, and HCl+SMT treated. NS, BIO, SUC, HCl were injected in to the lungs in a volume of 2 ml/kg. The rats received twice daily intraperitoneal injections of 20 mg(kg day) SMT (Sigma Chemical Co.) for 7 days. Seven days later, rats were killed, and both lungs in all groups were examined immunohistochemically and histopathologically. RESULTS: Our data show that SMT inhibits the inflammatory response significantly reducing (p<0.05) peribronchial inflammatory cell infiltration, alveolar septal infiltration, alveolar edema, alveolar exudate, alveolar histiocytes, interstitial fibrosis, granuloma, and necrosis formation in different pulmonary aspiration models. Furthermore, our data suggest that there is a significant reduction in the activity of iNOS and arise in the expression of surfactant protein D in lung tissue of different pulmonary aspiration models with SMT therapy. CONCLUSION: It was concluded that SMT treatment might be beneficial in lung injury, therefore shows potential for clinical use.

Differential effect of L-NAME and S-methyl-isothiourea on leukocyte emigration in carrageenin-soaked sponge implants in rat.[Pubmed:9283697]

Br J Pharmacol. 1997 Aug;121(8):1637-44.

1. The role of nitric oxide (NO) in leukocyte (polymorphonuclear cells, monocytes and lymphocytes) emigration was studied in a model of carrageenin-sponge implants in rats. 2. The subcutaneous implantation of 1% (w/v) of lambda-carrageenin-soaked sponges elicited an inflammatory response that was characterized by a time-related increase in leukocyte infiltration in the sponges and increased levels of nitrite in the exudate. Total leukocyte infiltration and nitrite production were maximal at 24 h and decreased after 48 and 96 h. The mononuclear cell influx was maximal at 48 h (21% of the total leukocytes). Therefore, this time point was used in the successive experiments. 3. Polymorphonuclear cell (PMN) and lymphocyte infiltration in the sponges significantly increased when rats were treated with the non-specific NO-synthase (NOS) inhibitor, NG-nitro-L-arginine methylester (L-NAME) (1 mg ml-1) in drinking water ad libitum). Monocyte emigration was not affected by L-NAME treatment. The nitrite levels in the exudate of L-NAME-treated rats were significantly reduced. The concomitant ingestion of L-arginine (30 mg ml-1) resulted in a reversion of the L-NAME effect, while D-arginine (30 mg ml-1) had no effect, indicating the involvement of the L-arginine: NO pathway. 4. Administration of L-NAME resulted also in an increased release of tumour necrosis factor-alpha (TNF-alpha) and prostacyclin (measured as the stable metabolite, 6-keto-PGF 1 alpha). L-NAME had no effect on monocyte chemoattractant protein-1 (MCP-1) release in the exudate. 5. Since L-NAME may have effects on the local blood flow, phenylephrine (0.034 mg ml-2) in drinking water) was used as it has an effect on the local blood flow similar to L-NAME. Phenylephrine had no effect on either leukocyte emigration, or on nitrite, TNF-alpha, prostacyclin or MCP-1 accumulation in the exudate. 6. In contrast, the more selective iNOS inhibitor S-methyl-isothiourea (SMT) (10 micrograms ml-1) in drinking water) significantly reduced PMNs and lymphocyte influx in the sponge having no effect on monocyte influx. Moreover, SMT decreased nitrite production in the exudate to a comparable extent as L-NAME. 7. Administration of SMT significantly reduced MCP-1 release in the exudate, without an effect on TNF-alpha or prostacyclin production. Moreover SMT did not produce any changes in local blood flow. 8. Our results show that a different outcome of the inflammatory process can be obtained depending on the types of NOS inhibitor used.

Isothioureas: potent inhibitors of nitric oxide synthases with variable isoform selectivity.[Pubmed:7533622]

Br J Pharmacol. 1995 Jan;114(2):510-6.

1. The induction of a calcium-independent isoform of nitric oxide (NO) synthase (iNOS) and a subsequent enhanced formation of NO has been implicated in the pathophysiology of a variety of diseases including inflammation and circulatory shock. Here we demonstrate that the S-substituted isothioureas, S-methylisothiourea (SMT), S-(2-aminoethyl)isothiourea (aminoethyl-TU), S-ethylisothiourea (ethyl-TU) and S-isopropylisothiourea (isopropyl-TU) potently inhibit iNOS activity in J774.2 macrophages activated with bacterial endotoxin with EC50 values 8-24 times lower than that of NG-methyl-L-arginine (MeArg) and 200-times lower than that of NG-nitro-L-arginine (L-NO2Arg). 2. The inhibition of iNOS activity by these S-substituted isothioureas is dose-dependently prevented by excess of L-arginine suggesting that these isothioureas are competitive inhibitors of iNOS at the L-arginine binding site. 3. Ethyl-TU and isopropyl-TU are 4-6 times more potent than MeArg in inhibiting the constitutive NOS activity in homogenates of bovine aortic endothelial cells (eNOS) and are more potent pressor agents than MeArg in the anaesthetized rat. SMT is equipotent with MeArg, whereas aminoethyl-TU is 6-times less potent in inhibiting eNOS activity in vitro. Both SMT and aminoethyl-TU, however, elicit only weak pressor responses (approximately 15 mmHg at 10 mg kg-1, i.v.) in vivo. 4. A comparison of the potencies of ethyl-, iso-propyl-, n-propyl-, t-butyl- and n-butyl-isothioureas on iNOS activity shows that the inhibitory activity of S-substituted isothioureas declines sharply if the side chain exceeds 2 carbon atoms in length. Similarly, substitution of the ethylene side chain of ethyl-TU also results in a diminished potency. Substitution of either one or both nitrogens of SMT with either amino or alkyl groups also substantially reduces its NOS inhibitory potency.5. In conclusion, isothioureas represent a new class of NOS inhibitors which includes the most potent inhibitors of iNOS activity reported to date. Some members of this class (ethyl-TU and isopropyl-TU)are potent inhibitors of eNOS and iNOS with little selectivity towards either isoform, while others (SMT and aminoethyl-TU) are relatively selective inhibitors of iNOS activity. These latter agents may become useful tools for studying the role of iNOS in various disease models and may be useful in the therapy of diseases that are associated with an enhanced formation of NO due to iNOS induction, such as inflammation, circulatory shock or cancer.