Effect of the cardioselective ATP-sensitive potassium channel inhibitor HMR 1883 in a porcine model of cardiopulmonary resuscitation

OBJECTIVE

HMR 1883 (the free acid form of HMR 1098) selectively inactivates myocardial ATP sensitive potassium channels, which may be a potential important therapeutic approach to prevent life-threatening arrhythmias. This study was designed to assess the effects of HMR 1883 combined with adrenaline on haemodynamic variables, blood gases, and cardiac arrhythmias in a porcine cardiac arrest model.

METHODS

After 8 min of untreated cardiac arrest, followed by 1 min of cardiopulmonary resuscitation (CPR), 12 pigs weighing 30-40 kg were assigned randomly to receive either 45 microg/kg adrenaline alone (n=6), or 45 microg/kg adrenaline combined with 3 mg/kg HMR 1883 (n=6), followed by up to three defibrillation attempts 2 min later. Five minutes after return of spontaneous circulation, cardiac arrest was induced for 1 min, with the CPR protocol following as described above. All animals subsequently underwent four cardiac arrest intervals of 1, 2, 3, and 4 min duration which were separated by four episodes of 5 min of return of spontaneous circulation.

RESULTS

Haemodynamic variables, cardiac arrhythmias in the acute resuscitation phase between termination of chest compressions and return of spontaneous circulation, and after return of spontaneous circulation in both groups were comparable throughout the experiment. Survival rates throughout the experiment were comparable between groups. Arterial blood gases, electrolyte, glucose, and lactate levels in both groups during the experiment indicated comparable severe metabolic acidosis, with increasing levels after each episode of simulated refibrillation, and subsequent return of spontaneous circulation.

CONCLUSION

Combining HMR 1883 with adrenaline during CPR resulted in comparable haemodynamic variables, return of spontaneous circulation rates, cardiac arrhythmias, lactate and glucose levels compared with adrenaline alone. This indicates that injection of HMR 1883 was safe under these conditions.

Alleviation of wood smoke-induced lung injury by tachykinin receptor antagonist and hydroxyl radical scavenger in guinea pigs

We recently reported that wood smoke inhalation initially (within 5 min) causes airway injury and subsequently produces both airway and parenchymal injury after a delay (within 2 h). In this study, we investigated the mediator mechanisms of this delayed smoke-induced lung injury in 126 anesthetized and artificially ventilated guinea pigs who received challenges of either air or 40 tidal breaths of wood smoke. Two hours after inhalation, wood smoke produced various injurious responses, including increases in alveolar-capillary permeability, microvascular permeabilities, and histological injury scores, in airway and parenchymal tissues. Pre-treatment given before smoke challenge with CP-96,345 [a tachykinin NK1 receptor antagonist; (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-aza bicyclo(2.2.2.)-octan-3-amine], dimethylthiourea (a hydroxyl radical scavenger), or a combination of these two drugs largely alleviated both the airway and parenchymal responses, whereas pre-treatment with SR-48,968 [a tachykinin NK2 receptor antagonist; (S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)-butyl)benzamide] or a combination of CP-96,344 and SR-48,965 (inactive enantiomers) failed to do so. Post-treatment given at 5 min after smoke challenge with CP-96,345 or dimethylthiourea significantly alleviated the parenchymal responses, while having no effect on the airway responses. Pre-treatment with dimethylthiourea prevented the smoke-induced reduction in airway neutral endopeptidase activity (an enzyme for tachykinin degradation). We concluded that (1) tachykinins and hydroxyl radical play important roles in producing smoke-induced delayed lung injury in guinea pigs, and both may be involved in the spread of injury from the airways to the pulmonary parenchyma, and (2) the contribution of tachykinins is mediated via the activation of tachykinin NK1 receptors, and is associated with the hydroxyl radical-induced inactivation of airway neutral endopeptidase.

Reactive oxygen species and endotoxic shock: effect of dimethylthiourea

The effects of endotoxemia on the cardiac function and contractility, oxygen radical production by polymorphonuclear leukocytes (PMNL-CL), cardiac antioxidant reserve (LV-CL), antioxidant enzymes (superoxide dismutase [SOD], catalase, glutathione peroxidase [GSH-P(X)]) and malondialdehyde (MDA); and plasma creatine kinase (CK) and lactate in the absence or presence of dimethylthiourea (DMTU), an antioxidant, in anesthetized dogs were studied. Dogs were assigned to three groups: group 1, control; group II, endotoxin (ET) (5 mg/kg body wt intravenously), and group III, ET + DMTU (500 mg/kg intravenously). ET produced decreases in the cardiac function and contractility, antioxidant reserve, antioxidant enzymes; and increases in PMNL-CL, cardiac MDA, plasma CK, and lactate. Pretreatment with DMTU attenuated the ET-induced cardiac dysfunction and changes in the cardiac MDA, antioxidant reserve, and antioxidant enzymes, PMNL-CL, and plasma CK and lactate levels. These results suggest that reactive oxygen species may be involved in the deterioration of cardiac function and contractility, and cellular injury during endotoxic shock and that antioxidants may be of value in the treatment of endotoxic shock.

KB-R7943, a selective Na+/Ca2+ exchange inhibitor, protects against ischemic acute renal failure in mice by inhibiting renal endothelin-1 overproduction

We investigated whether the preischemic or postischemic treatment with KB-R7943, a novel and selective Na+/Ca2+ exchange inhibitor, has renal protective effects in mice with ischemic acute renal failure (ARF). Ischemic ARF was induced by clamping the left renal pedicle for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function was markedly diminished 24 h after reperfusion. Preischemic treatment with KB-R7943 attenuated the ARF-induced renal dysfunction. The ischemia/reperfusion-induced renal dysfunction was also overcome by postischemic treatment with KB-R7943. Histopathologic examination of the kidneys of ARF mice revealed severe renal damage such as tubular necrosis, proteinaceous casts in tubuli, and medullary congestion. Histologically evident damage and Ca2+ deposition in necrotic tubular epithelium were improved by preischemic treatment with KB-R7943. In addition, preischemic treatment with KB-R7943 significantly suppressed the increment of endothelin-1 (ET-1) content in the kidney at 2, 6, and 24 h after reperfusion. These findings suggest that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by renal ET-1 overproduction, plays an important role in the pathogenesis of the ischemia/reperfusion-induced ARF. KB-R7943 may prove to be an effective therapeutic agent for cases of ischemic ARF in humans.

Antioxidant treatment inhibits activation of myocardial nuclear factor kappa B and inhibits nitrosylation of myocardial heme protein in cardiac transplant rejection

Nitric oxide production via inducible nitric oxide synthase (iNOS) is believed to play a role in cardiac allograft rejection. Previously, we showed that antioxidants can significantly prolong cardiac graft survival, but the nature of this protection is unknown. In the present study, we examined the protective effect of another antioxidant, dimethylthiourea (DMTU), in a model of cardiac allograft rejection. Specifically, we hypothesized that DMTU would prolong graft survival and decrease activation of nuclear factor-kappa B (NF-kappa B), an important redox-sensitive transcription factor necessary for iNOS gene expression. NF-kappa B was activated by twofold as early as postoperative day 2 in allografts. NF-kappa B activation in allografts progressed to a peak of ninefold by postoperative day and remained increased until postoperative day 6. No activation of NF-kappa B was observed in isografts for comparable time periods. Treatment with DMTU resulted in a significant prolongation of graft survival. This beneficial effect was associated with diminished activation of myocardial NF-kappa B. Treatment with DMTU also resulted in decreased formation of iron-nitrosylprotein complexes as evidenced by electron paramagnetic resonance spectroscopy. These studies provide evidence that reactive oxygen plays a significant role in signal transduction for activation via the transcription factor, NF-kappa B, thereby modulating distal actions and consequences of iNOS-derived nitric oxide.

Pre- or post-ischemic treatment with a novel Na+/Ca2+ exchange inhibitor, KB-R7943, shows renal protective effects in rats with ischemic acute renal failure

We investigated the effects of pre- or post-ischemic treatment with KB-R7943, a new Na+/Ca2+ exchange inhibitor, on ischemic acute renal failure (ARF) in rats, and these were compared with the effects of verapamil. Ischemic ARF was induced by clamping the left renal pedicle for 45-min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function markedly decreased 24 h after reperfusion. Pre-ischemic treatment with KB-R7943 or verapamil attenuated the ARF-induced renal dysfunction. The ischemia/reperfusion-induced renal dysfunction was overcome by post-ischemic treatment with KB-R7943 but not with verapamil. Histopathological examination of the kidney of ARF rats revealed severe renal damage, and suppression of the damage was seen with post-ischemic treatment with KB-R7943. KB-R7943 markedly suppressed the increment of endothelin-1 (ET-1) content in the kidney at 2, 6, and 24 h after reperfusion. No significant changes in Na+/Ca2+ exchanger protein expression in renal tissue were observed with 45-min ischemia, 6 h after reperfusion and KB-R7943 treatment. These results suggest that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by ET-1 overproduction, seems to play an important role in the pathogenesis of the ischemia/reperfusion-induced ARF. KB-R7943, which is effective in both cases of pre- and post-ischemic treatments, may prove to be an effective therapeutic agent for cases of ischemic ARF.

Novel class of thiourea compounds that inhibit herpes simplex virus type 1 DNA cleavage and encapsidation: resistance maps to the UL6 gene

In our search for novel inhibitors of herpes simplex virus type 1 (HSV-1), a new class of thiourea inhibitors was discovered. N-(4-[3-(5-Chloro-2,4-dimethoxyphenyl)-thioureido]-phenyl)-acetamide and its 2-fluoro-benzamide derivative inhibited HSV-1 replication. HSV-2, human cytomegalovirus, and varicella-zoster virus were inhibited to a lesser extent. The compounds acted late in the replication cycle by impairing both the cleavage of concatameric viral DNA into progeny genome length and the packaging of the DNA into capsids, indicative of a defect in the encapsidation process. To uncover the molecular target of the inhibition, resistant HSV-1 isolates were generated, and the mutation responsible for the resistance was mapped using marker transfer techniques. Each of three independent isolates had point mutations in the UL6 gene which resulted in independent single-amino-acid changes. One mutation was located in the N terminus of the protein (E121D), while two were located close together in the C terminus (A618V and Q621R). Each of these point mutations was sufficient to confer drug resistance when introduced into wild-type virus. The UL6 gene is one of the seven HSV-1 genes known to play a role in DNA packaging. This novel class of inhibitors has provided a new tool for dissection of HSV-1 encapsidation mechanisms and has uncovered a new viable target for the treatment of herpesviral diseases.

Treatment with dimethylthiourea prevents left ventricular remodeling and failure after experimental myocardial infarction in mice: role of oxidative stress

Oxidative stress might play an important role in the progression of left ventricular (LV) remodeling and failure that occur after myocardial infarction (MI). We determined whether reactive oxygen species (ROS) are increased in the LV remodeling and failure in experimental MI with the use of electron spin resonance spectroscopy and whether the long-term administration of dimethylthiourea (DMTU), hydroxyl radical (.OH) scavenger, could attenuate these changes. We studied 3 groups of mice: sham-operated (sham), MI, and MI animals that received DMTU (MI+DMTU). Drugs were administered to the animals daily via intraperitoneal injection for 4 weeks.OH was increased in the noninfarcted myocardium from MI animals, which was abolished in MI+DMTU. Fractional shortening was depressed by 65%, LV chamber diameter was increased by 53%, and the thickness of noninfarcted myocardium was increased by 37% in MI. MI+DMTU animals had significantly better LV contractile function and smaller increases in LV chamber size and hypertrophy than MI animals. Changes in myocyte cross-sectional area determined with LV mid-free wall specimens were concordant with the wall thickness data. Collagen volume fraction of the noninfarcted myocardium showed significant increases in the MI, which were also attenuated with DMTU. Myocardial matrix metalloproteinase-2 activity, measured with gelatin zymography, was increased with MI after 7 and 28 days, which was attenuated in MI+DMTU. Thus, the attenuation of increased myocardial ROS and metalloproteinase activity with DMTU may contribute, at least in part, to its beneficial effects on LV remodeling and failure. Therapies designed to interfere with oxidative stress might be beneficial to prevent myocardial failure.

[Acute myocardial ischemia and ventricular arrhythmias in the pathogenesis of sudden cardiac death in coronary disease]

There is increasing evidence for a fatal interaction of myocardial ischemia, ventricular arrhythmias and sudden cardiac death in some patients with coronary artery disease. Evidence comes from autopsy studies, from the evaluation of patients who survived an episode of sudden cardiac death, from follow-up data of these patients either treated or not by revascularization therapy and/or an implantable cardioverter-defibrillator and indicate that reducing the individual ischemic burden will be beneficial to reduce the incidence of sudden cardiac death. Studies in patients with stable and especially with unstable angina using Holter monitoring could demonstrate that there is a close and causal relationship between myocardial ischemia inducing or aggravating life-threatening ventricular arrhythmias and sudden cardiac death particularly in patients with unstable and postinfarction status. This review summarizes some of our clinical knowledge on this topic and indicates that preventive strategies for myocardial ischemia are the antiarrhythmic treatment of choice in patients with severe coronary artery disease and patients with evidence or at risk for ischemic proarrhythmia.

Wood smoke-induced airway hyperreactivity in guinea pigs: time course, and role of leukotrienes and hydroxyl radical

A prior airway exposure to wood smoke induces a tachykinin-dependent increase in airway responsiveness to the subsequent smoke inhalation in guinea pigs (Life Sci. 63: 1513, 1998). To further investigate the time course of, and the contribution of other chemical mediators to, this smoke-induced airway hyperresponsiveness (SIAHR), two smoke challenges (each 10 ml) separated by 30 min were delivered into the lungs of anesthetized guinea pigs by a respirator. In the control animals, the SIAHR was evidenced by the bronchoconstrictive response to the second smoke challenge (SM2) which was approximately 5.2-fold greater than that to the first challenge (SM1). This SIAHR was alleviated by shortening the elapsed time between SM1 and SM2 to 10 min or by extending it to 60 min, and was abolished by extending it to 120 min. This SIAHR was reduced by pretreatment with either MK-571 (a leukotriene D4-receptor antagonist) or dimethylthiourea (a hydroxyl radical scavenger), but was not affected by pretreatment with either pyrilamine (a histamine H1-receptor antagonist) or indomethacin (a cyclooxygenase inhibitor). The smoke-induced reduction in the neutral endopeptidase activity (a major enzyme for tachykinin degradation) measured in airway tissues excised 30 min post SM1 was largely prevented by pretreatment with dimethylthiourea. However, this reduction was not seen in airway tissues excised 120 min post SM1. These results suggest that 1) the SIAHR to inhaled wood smoke has a rapid onset time following smoke inhalation and lasts for less than two hours, 2) leukotrienes and hydroxyl radical may play contributory roles in the development of this SIAHR, and 3) hydroxyl radical is the major factor responsible for the smoke-induced inactivation of airway neutral endopeptidase, which may possibly participate in the development of this SIAHR.

[Electrophysiological evaluation of the protective effect of dimethylthiourea against retinal photic injury]

PURPOSE

The Protective effect of dimethylthiourea (DMTU) against photic injury of the retina was evaluated by electroretinogram (ERG).

METHODS

In the DMTU-treated group, 250, 500, or 750 mg/kg DMTU was administered intraperitoneally to albino rabbits at 24 hours and immediately before starting light exposure to the eye. In the control group, physiological saline was injected intraperitoneally instead of DMTU. Preservation rates of ERG a-, b- and c-wave amplitudes were defined as the percentages of the post-photic injury values to the pre-photic injury ones, and were compared between the control and the DMTU-treated groups.

RESULTS

In 750 mg/kg DMTU-treated group, the preservation rate of the a-wave was significantly higher than that in the control group 24 hours after the photic injury. While the preservation rate of the c-wave was remarkably low in the control group 24 hours after the photic injury, it was significantly higher in the 500 and 750 mg/kg DMTU-treated groups. Furthermore, better preservation rates of the c-wave were noted with higher doses of DMTU.

CONCLUSION

These results suggest that DMTU protects against photic injury of the retinal pigment epithelium and photoreceptors.

Attenuation of cisplatin-induced acute renal failure is associated with less apoptotic cell death

To clarify the pathophysiologic role of apoptosis in acute renal failure (ARF), we examined whether the attenuation of cisplatin-induced ARF is associated with the change in the degree of apoptotic cell death. The administration of cisplatin (CDDP) (6 mg/kg body weight) in rats induced ARF at day 5, as manifested by a significant increase in serum creatinine (Scr) and tubular damage. CDDP-induced apoptotic cell death was confirmed by electron microscopic examination, agarose gel electrophoresis, and increased cells positive for TaT-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) in the outer medulla of the kidney. Treatment with dimethylthiourea (DMTU)--a scavenger of hydroxyl radicals--or glycine abrogated CDDP-induced increases in Scr, the tubular damage score, and the number of TUNEL-positive cells. Pretreatment with uranyl acetate (UA) induced a significant expression of Bcl-2 in the kidney and ameliorated CDDP-induced increases in Scr, the tubular damage score, and TUNEL-positive cells in the outer stripe of the outer medulla. Our findings indicate (1) that the attenuation of CDDP-induced ARF was associated with less apoptotic cell death and (2) that the induction of the anti-apoptotic protein Bcl-2 attenuated apoptosis and tubular damage. Our results suggest that apoptotic cell death may play an important role in the development of cisplatin-induced ARF.

Comparison of intraocular treatment of DMTU and SOD following retinal ischemia in rats

The effect of intravitreal injections of DMTU (dimethylthiourea) and SOD (superoxide dismutase), two free radical scavengers, was evaluated in a rat model of retinal ischemia induced by elevated intraocular pressure. The drugs were administered just before or just after a 60 min ischemia. At days 2 and 7 after reperfusion, retinal recovery was evaluated by electroretinography. At day 7, layer thicknesses and cell rows were measured from histologic sections of paraffin-embedded retinas. In the vehicle-treated control group, we observed a decrease in the inner retinal layers and b-wave amplitude impairment. SOD injection (6 units/eye) protected the retina from ischemia/reperfusion injury. At day 2 after reperfusion, electroretinographic recovery was more efficient when SOD was administered just after ischemia (99%) than after pretreatment with SOD (81%) (p<0.03). In the DMTU-treated group (75 microg/eye), only the pretreatment induced significant electrophysiologic (40%) (p<0.001) and morphologic recovery.

ATP-sensitive potassium channel blocker HMR 1883 reduces mortality and ischemia-associated electrocardiographic changes in pigs with coronary occlusion

ATP-sensitive potassium (K(ATP)) channels are activated during myocardial ischemia. The ensuing potassium efflux leads to a shortening of the action potential duration and depolarization of the membrane by accumulation of extracellular potassium favoring the development of reentrant arrhythmias, including ventricular fibrillation. The sulfonylthiourea HMR 1883 was designed as a cardioselective blocker of myocardial K(ATP) channels for the prevention of arrhythmic sudden death in patients with ischemic heart disease. We investigated the effect of HMR 1883 on sudden cardiac arrhythmic death and electrocardiography (ECG) changes induced by 20 min of left anterior descending coronary artery occlusion in pentobarbital-anesthetized pigs. HMR 1883 (3 mg/kg i.v.) protected pigs from arrhythmic death (91% survival rate versus 33% in control animals; n = 12; p<.05). Ischemic areas were of a similar size. The compound had no effect on hemodynamics and ECG, including Q-T interval, under baseline conditions and no effect on hemodynamics during occlusion. In control animals, left anterior descending coronary artery occlusion lead to a prompt and significant depression of the S-T segment (-0.35 mV) and a prolongation of the Q-J time (+46 ms), the former reflecting heterogeneity in the plateau phase of the action potentials and the latter reflecting irregular impulse propagation and delayed ventricular activation. Both ischemic ECG changes were significantly attenuated by HMR 1883 (S-T segment, -0.14 mV; Q-J time, +15 ms), indicating the importance of K(ATP) channels in the genesis of these changes. In conclusion, the K(ATP) channel blocker HMR 1883, which had no effect on hemodynamics and ECG under baseline conditions, reduced the extent of ischemic ECG changes and sudden death due to ventricular fibrillation during coronary occlusion.

Inhibition of ciprofibrate-induced hepatocarcinogenesis in the rat by dimethylthiourea, a scavenger of hydroxyl radical

DNA damage caused by oxidative stress is considered to play an important role in peroxisome proliferator-induced hepatocarcinogenesis in rats and mice. In this study, we investigated the effect of dimethylthiourea (DMTU), a known hydroxyl radical scavenger, on ciprofibrate-induced hepatocarcinogenesis. Male F-344 rats were fed a diet containing 0.025% ciprofibrate and given daily intraperitoneal injections of DMTU (5 days a week) at a dose of 50 or 250 mg/kg body weight for 60 weeks at which time the study was terminated. Livers from all animals were analyzed grossly and microscopically for incidence, number and type of tumors. All rats given ciprofibrate alone developed altered areas, neoplastic nodules (NN) and hepatocellular carcinomas (HCC). Combined administration of ciprofibrate and DMTU resulted in inhibition of tumor development. In the group given higher doses of DMTU the incidence of NN was 100% and HCC 0%. The number of tumors per liver also significantly decreased (p<0.001). At lower dose levels DMTU caused significant reduction in the number of tumors per liver (p<0. 05) and a slight reduction (29%) in the incidence of HCC. The inhibitory effect of DMTU on ciprofibrate-induced hepatocarcinogenesis could be explained by hydroxyl radical scavenging properties of DMTU, resulting in decreased free radical induced DNA damage.

Chemoprevention of colonic aberrant crypt foci by an inducible nitric oxide synthase-selective inhibitor

Inducible nitric oxide synthase (iNOS) is overexpressed in colonic tumors of humans and also in rats treated with a colon carcinogen. iNOS appear to regulate cyclooxygenase-2 (COX-2) expression and production of proinflammatory prostaglandins, which are known to play a key role in colon tumor development. Experiments were designed to study the inhibitory effects of S,S'-1,4-phenylene-bis(1,2-ethanediyl)bis-isothiourea (PBIT) a selective iNOS-specific inhibitor, measured against formation of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF). Beginning at 5 weeks of age, male F344 rats were fed experimental diets containing 0 or 50 p.p.m. of PBIT, or 2000 p.p.m. of curcumin (non-specific iNOS inhibitor). One week later, rats were injected s.c. with AOM (15 mg/kg body wt, once weekly for 2 weeks). At 17 weeks of age, all rats were killed, colons were evaluated for ACF formation and colonic mucosa was assayed for isoforms of COX and NOS activities. Both COX and iNOS activities in colonic mucosa of the AOM-treated rats were significantly induced. Importantly, 50 p.p.m. PBIT suppressed AOM-induced colonic ACF formation to 58% (P < 0.0001) and crypt multiplicity containing four or more crypts per focus to 78% (P < 0.0001); it also suppressed AOM-induced iNOS activity. Curcumin inhibited colonic ACF formation by 45% (P < 0.001). These observations suggest that iNOS may play a key regulatory role in colon carcinogenesis. Developing iNOS-specific inhibitors may provide a selective and safe chemopreventive strategy for colon cancer treatment.

Glomerular overproduction of oxygen radicals in Mpv17 gene-inactivated mice causes podocyte foot process flattening and proteinuria: A model of steroid-resistant nephrosis sensitive to radical scavenger therapy

Focal segmental glomerulosclerosis is a steroid-resistant glomerular disease characterized by foot process flattening and heavy proteinuria. A similar disease was found to occur spontaneously in mice in which the Mpv17 gene was inactivated by retroviral insertion (Mpv17-/- mice). Here evidence is provided that glomerular damage in this murine model is due to overproduction of oxygen radicals and accumulation of lipid peroxidation adducts that were found in isolated glomeruli of Mpv17-/- mice. The development of glomerular disease in Mpv17-/- mice was inhibited by scavengers of oxygen radicals (dithiomethylurea) and lipid peroxidation (probucol), but not by steroid treatment. Although the glomerular polyanion was greatly reduced in proteinuric Mpv17-/- mice, it was preserved by antioxidative therapy. These results indicate that the glomerular disease in Mpv17-/- mice qualifies as a model of steroid-resistant focal segmental glomerulosclerosis and that experimental therapies with scavengers of oxygen radicals and lipid peroxidation efficiently ameliorate glomerular damage.

The effect of mannitol versus dimethyl thiourea at attenuating ischemia/reperfusion-induced injury to skeletal muscle

OBJECTIVE

Mannitol is used as a treatment for skeletal muscle ischemia/reperfusion (I/R) injury in humans, despite the fact that its effectiveness in vivo is still disputed. The purpose of this study was to determine the efficacy of mannitol in attenuating I/R injury at the microcirculatory level.

METHODS

The study was designed as an experimental study with male Wistar rats. The main outcome measures were intravital microscopy, which was used to measure capillary perfusion, capillary and venular red blood cell velocity (VRBC), and leukocyte-endothelial interactions in the extensor digitorum longus muscle of the rat hind limb before and after ischemia. In addition, tissue injury was assessed during reperfusion with the fluorescent vital dyes bisbenzimide and ethidium bromide. Dimethyl thiourea (DMTU), a highly effective therapeutic agent of experimental I/R injury, was used as a positive control.

RESULTS

No-flow ischemia (2 hour) resulted in a 40% drop in capillary perfusion, a decline in capillary and venular VRBC, and increased leukocyte venular adherence and tissue infiltration. Tissue injury increased to a constant level during reperfusion. Mannitol attenuated capillary malperfusion during the first 60 minutes of reperfusion and prevented a decline in capillary VRBC. However, mannitol did not reduce tissue injury or leukocyte adherence and infiltration during reperfusion. By comparison, DMTU not only prevented the perfusion deficits and the increases in leukocyte venular adherence and tissue infiltration but significantly reduced the magnitude of tissue injury.

CONCLUSION

Our findings suggest that mannitol may be of limited value for the prevention of early reperfusion-induced injury after no-flow ischemia in skeletal muscle. By comparison, DMTU was highly efficacious by not only reducing microvascular perfusion deficits but by also reducing leukocyte-endothelial cell interactions and the incidence of cellular injury.

Effects of histamine H3 receptor ligands in experimental models of anxiety and depression

Histamine H3 receptor ligands have been proposed to be of potential therapeutic interest for the treatment of different central nervous system disorders; however, the psychopharmacological properties of these drugs have not been studied extensively. In this work, we investigated the possible involvement of histamine H3 receptor function in experimental models of anxiety (elevated plus-maze) and depression (forced swimming test). Male Sprague-Dawley rats were treated i.p. with the histamine H3 receptor agonist R-alpha-methylhistamine (10 mg/kg) or the histamine H3 receptor antagonist thioperamide (0.2, 2 and 10 mg/kg) and 30 min afterwards the time spent in the open arms of an elevated plus-maze was registered for 5 min. The immobility time of male OF1 mice in the forced swimming test was recorded for 6 min, 1 h after the i.p. administration of R-alpha-methylhistamine (10 and 20 mg/kg), thioperamide (0.2, 2, 10 and 20 mg/kg) or another histamine H3 receptor antagonist, clobenpropit (5 mg/kg). The locomotor activity of mice was checked in parallel by means of an activity meter. Both saline controls and active drug controls were used in all the paradigms. Neither thioperamide nor R-alpha-methylhistamine significantly changed animal behaviour in the elevated plus-maze. R-alpha-methylhistamine and the higher dose of thioperamide assayed (20 mg/kg) were also inactive in the forced swimming test. By contrast, thioperamide (0.2-10 mg/kg) dose-dependently decreased immobility, the effect being significant at 10 mg/kg (33% reduction of immobility); clobenpropit produced an effect qualitatively similar (24% reduction of immobility). None of these histamine H3 receptor antagonists affected locomotor activity. These preliminary results suggest that the histamine H3 receptor blockade could be devoid of anxiolytic potential but have antidepressant effects. Besides, the stimulation of these receptors does not seem to be followed by changes in the behavioural parameters studied.

Ultrastructural study of calcium shift in ischemic/reperfused rat heart under treatment with dimethylthiourea, diltiazem and amiloride

Among factors underlying reperfusion injury are oxygen free radicals and Ca2+ influx via gated calcium channel or via Na+/H(+)-Na+/Ca2+ exchange which lead to calcium overload. The aim of the study was to ultrastructurally visualize the distribution of Ca2+ and to compare binding of calcium by the sarcolemma and calcium accumulation in mitochondria under therapy with an OH scavenger, dimethylthiourea (DMTU), Na+/H+ exchange inhibitor, amiloride, and calcium channel blocker, diltiazem, given alone or in combination to ischemic/reperfused hearts. Isolated working hearts subjected to 40 min ischemia and 30 min reperfusion were perfused with drugs added to the perfusate 15 min before ischemia and administered for the rest of the perfusion period. The cytochemical phosphate pyroantimonate method for localization of Ca2+ was used, and calcium distribution was analyzed with a computer image analyzer. All drugs given alone improved sarcolemmal ability to bind calcium. The best results were obtained with amiloride. All of the combined therapies gave even better results, but calcium accumulation in mitochondria diminished only with diltiazem therapy given alone or in combination with DMTU. Since the presence of Ca2+ deposits on the sarcolemma is believed to represent its normal function, and calcium sequestration by mitochondria reflects an increase in cytosolic calcium load, the lack of correlation between sarcolemmal and mitochondrial Ca2+ distribution might suggest impaired mechanisms of lowering cytoplasmic calcium or the existence of some mechanism other than Na+/Ca2+ exchange, mediated by activated Na+/H+ exchange.

Further in vivo studies on attenuating morphine withdrawal: isoform-selective nitric oxide synthase inhibitors differ in efficacy

The N-methyl-D-aspartate (NMDA) receptor-nitric oxide (NO) pathway has been linked to opiate withdrawal. Pretreatments with four inhibitors of NO synthase, 7-nitro indazole, 3-bromo-7-nitro indazole, S-methyl-L-thiocitrulline and aminoguanidine, which exhibit different isoform selectivity in vitro, were evaluated for their ability to attenuate signs of naloxone-precipitated morphine withdrawal. In separate experiments, effects of NO synthase inhibitors on blood pressure were measured in naive and morphine-dependent rats. 7-Nitro indazole, 3-bromo-7-nitro indazole and S-methyl-L-thiocitrulline, which are specific inhibitors of the constitutive isoforms, produced dose-dependent reductions of several signs of withdrawal. Blood pressure was unaffected by the indazoles, whereas S-methyl-L-thiocitrulline produced a strong vasoconstrictor response. Aminoguanidine, which selectively inhibits inducible NO synthase, reduced fewer signs of opioid withdrawal, had a lower relative potency and exhibited no vasopressor activity. These data suggest that constitutive isoforms, but not the inducible isoform of NO synthase, have a primary role in NO-mediated processes that modulate the opioid withdrawal syndrome in the rat.

Anticonvulsant activity of pyrid-3-yl-sulfonyl ureas and thioureas

The N-[(4-cycloheptylaminopyrid-3-yl)sulfonyl]-N'-cycloheptyl urea, a neuroprotective agent, and 10 chemically related sulfonyl(thio)ureas were evaluated in the maximal electroshock seizure test in mice. This sulfonylurea, BM 27, and two structurally related sulfonylthioureas, BM 11 and BM 34, emerged with a 50% effective dose (ED50) of 2.87, 1.72, and 1.19 mg/kg, respectively. Their anticonvulsant profiles were found to be similar to that of phenytoin: active in the maximal electroshock seizure (MES) test and inactive in chemically induced seizures (pentetrazole, strychnine, bicuculline, picrotoxine, N-methyl-D,L-aspartic acid). These compounds exhibited a higher protective index and potency than those of phenytoin. Additional work remains necessary, however, to determine whether BM 27 is of clinical interest.

Combined non-steroidal therapy in experimental corneal injury

PURPOSE

The effects of anti-inflammatory non-steroidal therapy combined with free-radical scavengers were studied and compared to corticosteroid use in the treatment of experimental corneal injury.

METHOD

Eighty New Zealand albino rabbits were used in this study. A corneal alkali burn was induced by applying 1-N NaOH filter paper on the central axis of the right cornea for 30 s. Animals were distributed into five treatment groups: group 1 (control group) was only given gentamicin; group 2 was treated with 0.5% dimethylthiourea (DMU); group 3 received 1% dexamethasone; group 4 was given combined 0.5% DMU and 1% indomethacin; group 5 was treated with 0.5% DMU and 0.1% diclofenac sodium. One 50-microliter drop of gentamicin was instilled every 12 h, whereas the other drugs were instilled every 6 h (50 microliters). All groups received the same antibiotic treatment as the control group. The animals were killed on the 5th day. Inflammatory index, area and perimeter of the wounded corneal zone, and corneal transparency were evaluated.

RESULTS

No significant differences in the inflammatory index were found between the treatment groups and the control group after 72 h. Significant differences (p < 0.001) were observed at 24 h in groups 3-5 when compared with the control group. Planimetry showed significant differences in group 4 when compared with the other groups (p < 0.05). Corneal transparency study showed statistically significantly better values in groups 4 and 5, when compared with the other groups, including group 3 (p < 0.05).

CONCLUSIONS

The use of 0.5% DMU combined with 1% indomethacin can be considered an alternative to corticosteroid treatment in our experimental chemical corneal injury.

Chronic treatment in vivo with dimethylthiourea, a hydroxyl radical scavenger, prevents diabetes-induced endothelial dysfunction

Oxidative stress is believed to play a role in diabetes-induced vascular complications. In this study, we tested whether chronic treatment with a known hydroxyl radical scavenger, dimethylthiourea (DMTU), could prevent endothelial dysfunction in diabetes. Lewis strain rats were made diabetic by an intravenous injection of streptozotocin. A subgroup of diabetic animals received daily intraperitoneal injections of 50 mg/kg DMTU beginning at 72 h after streptozotocin and throughout 8 weeks of diabetes. Diabetes caused an increase in aortic catalase activity (an index of compensatory in vivo oxidative stress) that was not prevented by long-term DMTU treatment. Long-term treatment of diabetic animals with DMTU did not alter serum insulin levels, blood glucose concentrations, or total glycosylated hemoglobin. Descending thoracic aortas were isolated, sectioned into rings and suspended in isolated tissue baths, and contracted with a submaximal concentration of norepinephrine. Relaxation to the endothelium-dependent vasodilator, acetylcholine, was impaired in diabetic aortas, whereas relaxation to A23187 and nitroglycerin was unaltered. DMTU treatment prevented the diabetes-induced impairment in endothelium-dependent relaxation to acetylcholine but had no effect on relaxations induced by either A23187 or nitroglycerin. These data suggest that chronic exposure to increased levels of hydroxyl radicals in vivo likely play a significant role in the origin of diabetes-associated endothelial dysfunction.

EUK-8 a synthetic catalytic scavenger of reactive oxygen species protects isolated iron-overloaded rat heart from functional and structural damage induced by ischemia/reperfusion

The effects of EUK-8, a synthetic, catalytic scavenger of reactive oxygen species, on isolated iron-overloaded rat hearts submitted to ischemia-reperfusion were studied. In the absence of EUK-8, functional parameters (systolic and diastolic pressures, oxygen consumption as estimated by the product heart rate times left ventricular diastolic pressure) were severely impaired 1 minute and 15 minutes after reperfusion following a 15 minute ischemic episode. Dimethylthiourea (10 mM), a hydroxyl radical scavenger, had a minimally protective effect. In contrast, EUK-8 at a concentration of 50 microM in the perfusion medium maintained these parameters at close to their preischemia values. Electron microscopic analysis of heart tissues after 15 minutes ischemia followed by 15 minutes reperfusion showed extensive damage to mitochondria and sarcomeres in untreated hearts, while the extent of damage was significantly lower in EUK-8-treated hearts. The functional and structural protection afforded by EUK-8 were significantly better than those induced by dimethylthiourea. These data suggest that EUK-8 may be therapeutically useful in preventing heart damage induced by ischemia-reperfusion, for example, during thrombolytic treatment of myocardial infarction.

Free radical-mediated vascular injury in lungs preserved at moderate hypothermia

BACKGROUND

Early allograft dysfunction remains a frequently encountered problem in clinical lung transplantation. Lung ischemia-reperfusion injury is associated with increased vascular permeability, which may be due in part to oxygen (O2) free radicals. However, it is not clear whether O2 free radicals are produced during ischemia under storage conditions in clinical lung transplantation.

METHODS

Using an isolated ex vivo rabbit lung model, we studied the effects of preservation temperature on pulmonary capillary filtration coefficient (Kf) and lipid peroxidation in rabbit lungs inflated with 100% O2 after preservation with or without the O2 free radical scavenger dimethylthiourea. New Zealand white rabbits weighing 2.7 to 3.1 kg were intubated and ventilated with room air or 100% O2 (tidal volume = 25 mL). After heparinization and sternotomy, the pulmonary artery was flushed with low-potassium-dextran-1% glucose solution (200 mL). The heart-lung block was excised, submerged, and stored for 24 hours at 1 degree or 10 degrees C. After 24-hour preservation, the heart-lung block was suspended from a strain-gauge force transducer and ventilated with room air. The pulmonary artery cannula was connected to a reservoir of hetastarch solution. The lungs were flushed briefly with the hetastarch solution, and the reservoir was raised sequentially at 8-minute intervals to achieve 1.0 to 1.5 mm Hg increments in pulmonary artery pressure. Lung weight gain, airway pressure, pulmonary artery pressure, and left atrial pressure were measured continuously. The slope of steady-state lung weight gain was used to determine Kf (g.min-1.cm H2O-1 x 100 g-1 wet weight).

RESULTS

Twenty-four-hour lung preservation at both 1 degree and 10 degrees C increased Kf. A similar increase in Kf was observed in lungs stored at 1 degree C while inflated with 100% O2. However, a significant increase in Kf was observed when lungs inflated with 100% O2 were stored at 10 degrees C. This increase in Kf was ameliorated by dimethylthiourea. Thiobarbituric acid-reactive substance levels were increased in lungs stored at 10 degrees C while inflated with 100% O2. This finding was eliminated by dimethylthiourea.

CONCLUSIONS

These results indicate that free radical injury occurs during the ischemic phase when lungs are stored at moderate hypothermia while inflated with 100% O2.

Combined therapy with dimethylthiourea, diltiazem and amiloride/dimethylamiloride in the ischemic/reperfused heart

OBJECTIVES

The relative contribution of oxygen free radicals, disturbances in calcium homeostasis and Na+/H+ exchange in the development of injury in the ischemic/reperfused heart was investigated. The study was designed to assess whether these factors initiate independent mechanisms of injury or, alternatively, they share a common mechanism of toxicity.

METHODS

Isolated working rat hearts were subjected to different periods (30-55 min) of global ischemia and then were reperfused for 30 min. We compared the effects of oxygen radical scavengers (10 mM dimethylthiourea, DMTU and 0.6 mM desferrioxamine), inhibitors of Na+/H+ exchange (0.15 mM amiloride and 15 microM dimethylamiloride, DMA) and of 0.1 microM diltiazem, which was used to limit calcium overload, given alone or in combination, on the rate of myocardial injury development (recovery of hemodynamic function, LDH release, incidence of severe arrhythmias and structural integrity of cardiomyocytes were estimated at reperfusion following different periods of ischemia).

RESULTS

All interventions studied, when given alone, provided nearly equivalent cardioprotection. DMTU or desferrioxamine when applied in combination with diltiazem provided additive cardioprotection, relatively limited, however, as compared to the remarkable cardioprotection achieved by DMTU or desferrioxamine in combination with amiloride.

CONCLUSIONS

All mechanisms studied may contribute in an equal manner to the rate of injury development in the ischemic/reperfused heart. The oxygen free radicals-induced myocardial injury may be partially attributed to some disturbance in intracellular calcium homeostasis, possibly calcium overload, whereas the damaging effect of the Na+/H+ exchange activated upon reperfusion is probably largely related to some other mechanism.

Long-term treatment with dimethylthiourea inhibits the development of autoimmune disease in NZB x NZWF1 mice

Long-term treatment with dimethylthiourea (DMTU), a scavenger of hydroxyl radical (.OH) and hypochlorous acid (HOCl), suppressed the age-related development of autoimmune disease in NZB x NZWF1 mice. Treatment reduced autoantibody production, retarded increase in blood urea nitrogen, and prolonged life. The results suggest that .OH and HOCl may, at least in part, enhance the development of autoimmune diseases in NZB x NZWF1 mice.

Role of oxygen-derived metabolites in the rat gastric mucosal injury induced by nitric oxide donors

Local intra-arterial infusion of high doses of the nitric oxide (NO) donor, nitroprusside (10-40 micrograms kg-1 min-1 for 15 min) induced dose-dependent haemorrhagic injury to the rat gastric mucosa and reduced systemic arterial blood pressure, whereas intragastric nitroprusside (10-50 mg ml-1), which caused similar falls in blood pressure, failed to induce such injury. The mucosal damage induced by nitroprusside was reduced by local concurrent infusion of superoxide dismutase (500-4000 i.u. kg-1). Local superoxide dismutase also abolished the mucosal injury induced by local infusion of the NO donor, S-nitroso-N-acetyl-penicillamine (40 micrograms kg-1 min-1), but not that induced by local infusion of endothelin-1 (5 pmol kg-1 min-1) indicating specific actions. Intravenous infusion of the iron chelator and peroxyl scavenger, desferrioxamine (0.25-1 mg kg-1 min-1) or the hydroxyl radical scavenger, dimethylthiourea (20 mg kg-1 min-1) also reduced the mucosal damage induced by the local administration of the NO donors, but not that induced by endothelin-1. These findings implicate the involvement of superoxide and possibly other oxygen-derived free radicals in the injurious actions of high levels of nitric oxide generated from NO donors, and may reflect a role of the cytotoxic peroxynitrite moiety.

Antioxidant therapy partially blocks immune-induced lung fibrosis

A mouse model of hypersensitivity pneumonitis was generated by challenge with a thermophilic actinomycete. Oxygen radical scavengers were administered to challenged mice: vitamin E at 1000 units daily, polyethylene glycol-superoxide dismutase (SOD) at 500 units daily, polyethylene glycol-catalase at 10,000 units daily, 1,3,dimethyl-2-thiourea (DMTU) at 2 mg daily, and the biomimetic SOD, copper(II) [diisopropyl salicylate]2 (CuDIPS) at 1 mg daily. At three weeks after actinomycete challenge, a 10-fold increase in bronchoalveolar (BAL) cell number was observed. Treatments with catalase or DMTU were without effect on the BAL cell number in challenged mice. However, infusion of vitamin E was associated with an increased BAL cell influx (15-fold increase at two and three weeks). Similarly, treatment with PEG-SOD and CuDIPS resulted in an increase in cell number at two and three weeks. PEG-SOD or CuDIPS treatment resulted in a strong neutrophilia, whereas control challenged mice had a cellular influx mostly of macrophages and lymphocytes. Vitamin E treatment of challenged mice led to an increased T lymphocyte recruitment at two and three weeks. In vitro studies showed that actinomycete challenge was associated with an enhancement of alveolar macrophage O2- release, which was blocked by PEG-SOD, vitamin E, or DSC treatment but was unaffected by catalase or DMTU treatment. In control challenged mice, there was a 25-fold increase in the BAL albumin concentration at two weeks. PEG-SOD, vitamin E, or CuDIPS treatment all decreased the albumin concentration; the three modulators also diminished lung fibrosis at two or three weeks, as seen by a decrease in lung hydroxyproline and collagen synthesis by lung fibroblasts. Examination of sections from lungs of challenged animals showed evidence of cellular infiltrates around the bronchi and the blood vessels. Challenged mice given continuous infusions of vitamin E, SOD, or CuDIPS had lung histological scores that were significantly lower than control challenged mice or challenged mice treated with catalase or DMTU. Thus, therapies based on O2- scavenging or treatment with a general antioxidant such as vitamin E may hold some promise in the treatment of hypersensitivity pneumonitis.

Effect of topical antioxidant therapy on experimental infectious keratitis

To test the effect that the treatment with topical antioxidants may have on corneal infection, we have studied the effect of topically applied antioxidants, such as dimethylthiourea 0.5% (DMTU) and dismutase superoxide 0.2% (SOD), on infectious experimental keratitis caused by Staphylococcus aureus. We have quantified the results of the incubated corneas in ex vivo as well as in in vivo treated with antioxidants by using the luminol amplified chemiluminescence technique (LAC). The evaluation of corneal inflammation was performed calculating the average inflammatory index obtained from the clinical observation of the corneal secretion, corneal edema and ciliary injection. The evolution of the corneal infiltration was evaluated by means of computerized planymetry. The antioxidants used in this study demonstrated a significant reduction of the LAC values when compared with a control group both in the in vivo as well as in ex vivo studies. No significant differences in the clinical evaluation of the average inflammatory index were observed between the study and the control groups. However, a significant increase in the corneal infiltration was registered in the antioxidant treated group (p < 0.001) evaluated by computerized planymetry. Our results indicate that the use of antioxidants as antiinflammatory drugs may have a potential negative influence on the course of infectious keratitis.

Increased glomerular and urinary malondialdehyde in puromycin aminonucleoside-induced proteinuria in rats

Puromycin aminonucleoside (PAN)-induced proteinuria in rats may be mediated by reactive oxygen metabolites (ROM), which are injurious to several cell components including membrane lipids. Increased malondialdehyde (MDA) production is indicative of lipid peroxidation. We examined if MDA content of glomeruli and its urinary excretion were increased in rats administered PAN. Of three groups of 8 Sprague-Dawley rats each, group 1 served a control, group 2 animals received a single intravenous injection of PAN (5 mg/100 g body weight) and group 3 animals PAN with intraperitoneal injections of dimethylthiourea (DMTU), a free radical scavenger of oxidants such as hydroxyl radicals, for 4 days. The rats were sacrificed on day 8 after PAN injection. Increasing proteinuria, starting on day 4, developed in animals in group 2 but not in the others. The glomerular MDA (nmol/mg protein) in group 2 animals was 2.93 +/- 1.91, significantly higher than 0.87 +/- 0.63 and 1.26 +/- 0.76 in groups 1 and 3, respectively. Urinary levels of MDA markedly increased in group 2 rats on day 3 and remained high thereafter, but no such increase occurred in the control animals and those administered PAN with DMTU; the latter was thus protective against PAN toxicity. Our observations support the view that ROM are involved in PAN-induced glomerular injury and that increased urinary MDA excretion can be a marker of ROM-mediated lipid peroxidation.

Antioxidant therapy in the treatment of experimental acute corneal inflammation

To ascertain the effectiveness of topical antioxidant therapy on acute corneal inflammation, we have studied the effectiveness of topical treatment with a saline solution and with antioxidants such as 0.2% superoxide dismutase and 0.5% dimethylthiourea (DMTU) in a controlled experimental study. The evolution of the inflammatory process was evaluated by a multimodel approach, including computer-assisted planimetry of the corneal ulcer and infiltrate, ultrasonic pachymetry, luminol-amplified chemiluminescence and the study of corneal transparency by direct spectral spectrophotometry transmittance. The experimental model was a corneal ulcer created by a 60-second application of 1 N sodium hydroxide. Topical treatment with DMTU was shown to significantly improve all parameters tested, while superoxide dismutase reduced only the corneal ulcers. Antioxidant topical therapy with DMTU was shown to be efficient in reducing the inflammatory reaction that occurs during acute corneal inflammation. This suggests that antioxidant therapy could be considered as a complementary treatment in the pharmacological modulation of acute corneal inflammation.

Synergistic effects of fish oil diet and dimethylthiourea in acute adriamycin nephrosis

The synergistic effects of combining fish oil (FO) diet, which reduces thromboxane A production, with the free radical scavenger, dimethylthiourea (DMTU), were evaluated in acute adriamycin nephrosis, because proteinuria in adriamycin nephrosis is mediated by increased renal thromboxane A and free radical production. The effects of combined evening primrose oil (EPO) and DMTU were compared with the DMTU + FO combination because EPO increases prostaglandin E but not thromboxane A. After 7, 14, and 21 days, proteinuria was significantly (p < 0.05) reduced in rats receiving either DMTU + corn oil (CO) or DMTU + FO compared with untreated control rats. However, after 21 days, rats receiving DMTU + FO had significantly reduced urine protein excretion compared with those receiving DMTU + CO (103.9 +/- 20 mg daily vs 351.8 +/- 29.8 mg daily; P < 0.05). In contrast to FO, rats receiving EPO + DMTU had similar urine protein excretion to rats receiving DMTU + CO after 21 days (170.2 +/- 20.34 mg daily vs 179.45 +/- 26.38 mg daily). The mean serum cholesterol concentration was significantly (P < 0.01) reduced in rats receiving DMTU + FO (195.2 +/- 23.8 mg/dL) compared with DMTU + CO (377.9 +/- 28.5 mg/dL). Serum triglyceride levels also were significantly (P < 0.01) reduced in rats receiving DMTU + FO (52.5 +/- 26.4 mg/dL) compared with DMTU + CO (100.5 +/- 36.9 mg/dL). No significant differences in serum cholesterol concentrations or triglycerides occurred between rats receiving DMTU + CO and DMTU + EPO. Renal glutathione content was significantly (P < 0.05) increased by 23% in normal rats receiving FO diet and by 34% in rats receiving combined DMTU + FO compared with CO alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of adjuvant arthritis in rats by treatment with oxygen radical scavengers

The contribution of reactive oxygen species (ROS), in particular hydroxyl radical (OH.), to joint inflammation was examined in rats developing adjuvant arthritis (AA) by treatment with ROS scavengers dimethylthiourea (DMTU) and DMSO. Adjuvant arthritis was induced in Sprague-Dawley (SD) rats by a single intradermal (i.d.) injection of Mycobacterium tuberculosis (MT) in oil on day 0. By day 14, all rats exhibited arthritis in the hindlimbs and the majority had involvement of the forelimbs. A marked inflammatory cell influx (75% neutrophils) was present in the synovial fluid. These cells, in vitro, spontaneously produced OH. (0.96 +/- 0.28 OH. units/h per 10(5) cells). In contrast, spontaneous OH. production by normal circulating leucocytes was absent (0.07 +/- 0.03 OH. units/h per 10(5) cells). Adjuvant-injected rats were treated with DMTU (500, 250 and 100 mg/kg), DMSO (330 and 165 mg/kg) or saline (disease control) once daily on days 8, 9 and 10 and twice daily on days 11, 12 and 13 postadjuvant injection. Both DMTU and DMSO significantly reduced the clinical evidence of arthritis (clinical scores: DMTU [500 mg/kg] = 0, P < 0.0001; DMSO [3.0 mL/kg] = 0.4 +/- 0.3, P < 0.01, compared with disease control = 2.3 +/- 0.3). Synovial fluid cell accumulation was also significantly reduced (DMTU [500 mg+kg] = 0.5 +/- 0.1 x 10(5) cells/four joints, P < 0.0001; DMSO [3.0 mL/kg] 2.75 +/- 1.9 x 10(5) cells/four joints, P < 0.01 compared with disease control = 11.76 +/- 1.7 x 10(5) cells/four joints). Neither treatment inhibited cutaneous delayed type hypersensitivity (DTH) to the disease inducing antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of blood glucose in the dimethylthiourea-induced protection against alloxan-induced diabetes

Dimethylthiourea (DMTU, 4.0 mmol/kg) injected into mice 30 min prior to alloxan injection markedly protected mice against the diabetogenic actions of 75 mg/kg alloxan. At 30 min after the above dose of DMTU alone (no alloxan), there was a marked rise in blood glucose. Mannoheptulose, an antagonist of glucose action at pancreatic beta-cells, when given 24 min after DMTU and 6 min before alloxan, eliminated the DMTU-induced protection. The protection was also removed in the fasted mice in which DMTU did not cause hyperglycemia. These results indicate that DMTU protected mice from alloxan-induced diabetes by the indirect mechanism of producing hyperglycemia at the time of alloxan injection.

Novel [2-(4-piperidinyl)ethyl](thio)ureas: synthesis and antiacetylcholinesterase activity

A series of 1-ar(o)yl-3-[2-(1-benzyl-4-piperidinyl)ethyl](thio)urea derivatives was synthesized and evaluated for antiacetylcholinesterase activity. Most aroyl(thio)urea derivatives showed potent inhibitory activity in the sub-micromolar range. A comparable potency was obtained with the aryl(thio)urea analogues by replacing the phenyl with a 2-pyridyl group. The substituted guanidine variations proved to be almost inactive whereas the nitroethylene analogues appeared to be quite efficient. These results were interpreted in terms of the preferential cis-trans conformation of the aroyl(thio)urea and 2-pyridyl(thio)urea moieties involving the existence of hydrogen bonding. In vivo experiments showed that compound 7m had maximal antiamnestic activity at 0.03 mg/kg with a therapeutic ratio greater than 1000, while cholinergic side effects were only seen at doses 100-fold the maximally effective antiamnestic dose. Compound 7m represents a potentially interesting antidementia agent.

Glycerol-induced augmentation of sensitivity to endotoxin in rats

Combined sepsis and rhabdomyolysis result in a mortality rate much higher than that caused by each process alone. An analogous rat model is obtained by simultaneous i.p. administration of a nonlethal dose of lipopolysaccharide (LPS 0.025 mg/100 g) and a nonlethal i.m. injection of glycerol (1 ml/100 g). The aim of this study was to determine the factors contributing to the high mortality rate in this rat model. The factors examined include: Dehydration, plasma volume expansion, 'immunization' to glycerol, induction of LPS tolerance and the effect of free radicals formed in this model. Neither dehydration nor volume expansion affected mortality. 'Immunization' with glycerol was also not effective. In contradistinction, tolerance to LPS achieved by a daily injection with gradual increasing doses of LPS (from 0.05 mg/100 g to 1 mg/100 g) for 6 days reduced the mortality rate by 60% (P < 0.001). Moreover, decreasing free radical activity using the natural antioxidant (NAO) (5 mg/100 g) reduced mortality rates by 50%. A different antioxidant, dimethylthiourea (DMTU) (50 mg/100 g) failed to reduce mortality rates. This study suggests that the synergism between glycerol and LPS is apparently due to an increase in the rats' sensitivity to endotoxin following glycerol injection. However, endotoxin apparently does not enhance sensitivity to glycerol in the rat. The new antioxidant NAO significantly reduced the high mortality rate.

Roles of hemodynamic and tubular factors in gentamicin-mediated nephropathy

Gentamicin (GM) often causes polyuric acute renal failure (ARF) in humans and animals. GM-mediated ARF in rats was accompanied with activated renin-angiotensin system, increased renal endothelin content, and enhanced lipid peroxidation. Suppression of the renin-angiotensin activity by desoxycorticosterone acetate and saline drinking, and treatment with superoxide dismutase attenuated the GM-induced decline in whole-kidney GFR with well-maintained RBF but did not reduce the severity of tubular necrosis. On the other hand, treatment with dimethylthiourea, a hydroxyl radical scavenger, attenuated the GM-mediated decline in GFR and lessened tubular necrosis but did not ameliorate the reduction in RBF. These data suggest contributions of both vascular and tubular factors to the GM-induced decline in GFR in rats. However, relative importance of these factors probably differs with different doses of the agent.

23Na-NMR detects hypoxic injury in intact kidney: increases in sodium inhibited by DMSO and DMTU

Hypoxic injury in the isolated perfused rat kidney (IPRK) was monitored using 23Na-NMR in the presence or absence of 1.5 and 15 mM dimethylthiourea (DMTU) or 15 mM dimethylsulphoxide (DMSO) before and after inducing hypoxia. Hypoxia induced a prompt exponential increase in total renal 23Na+, renal vascular resistance, and sodium excretion and decreased inulin clearance and adenine nucleotides and reduced glutathione concentrations. Lipid peroxide metabolites were unaltered. The increase in 23Na+ was significantly reduced (P < 0.001) by both DMTU and DMSO although hypoxic perturbations of function and biochemical parameters were not. Posthypoxic increases in renal 23Na+ include approximately 10% from the intratubular compartment, but principally reflect the intracellular and interstitial compartments. The results demonstrate that 23Na-NMR is a sensitive indicator of hypoxic renal injury in intact kidney and suggest that DMTU and DMSO protect against hypoxic injury by a mechanism independent of free radical-binding.

Coronary vascular injury following transient coronary artery occlusion: prevention by pretreatment with deferoxamine, dimethylthiourea and N-2-mercaptoproprionyl glycine

The role of oxygen-derived free radicals as initiators of vascular dysfunction observed 24 hr after transient coronary artery occlusion (15 or 30 min) was examined in the anesthetized dog. A 15-min occlusion increased human serum (HSA) albumin extravasation within anterior myocardium without producing myocardial necrosis or edema. Minimal leukocyte uptake and free radical formation were present at 24 hr. 2-Mercaptoproprionyl glycine (MPG) (a free radical scavenger), deferoxamine (a chelator of ferrous ions) and dimethylthiourea (a hydroxyl ion scavenger), administered 15 min before coronary artery occlusion and extending 1.5 hr into reperfusion, reduced HSA uptake within anterior myocardium. A different pattern of injury was present after a 30-min occlusion. Subendocardial necrosis (1.2 +/- 0.8 g), edema, HSA extravasation and leukocyte uptake were observed at 24 hr. MPG failed to reduce the extent of necrosis, HSA extravasation, edema, leukocyte uptake or free radical formation. HSA extravasation, leukocyte uptake, tissue edema and free radical formation present 24 hr after a 30-min occlusion were reduced by acute deferoxamine and dimethylthiourea, but not by acute MPG administration. The failure of MPG to reduce HSA extravasation observed 24 hr after a 30-min coronary artery occlusion was associated with both leukocyte uptake and continued free radical formation, whereas dimethylthiourea and deferoxamine reduced leukocyte uptake, free radical formation and HSA extravasation.

Free radicals and brain damage due to transient middle cerebral artery occlusion: the effect of dimethylthiourea

The objective of this study was to assess whether dimethylthiourea (DMTU), an established free radical scavenger, ameliorates ischaemic damage due to 2-3 h of transient middle cerebral artery (MCA) occlusion, induced by an intraluminal filament. A major point addressed was whether DMTU given before MCA occlusion only delayed the "maturation" of the damage, or if it had a lasting effect on infarct size. The end point was morphological, and either encompassed triphenyltetrazolium chloride (TTC) staining of tissue slices after 24 h or 48 h of recovery, or histopathological assessment of infarct size after 7 days of recovery. In a preliminary series of experiments, rats were subjected to 3 h of MCA occlusion, and infarct volume was assessed by TTC staining after 24 h of recovery. DMTU in a dose of 750 mg/kg reduced infarct volume by more than 50%. However, due to a high mortality rate, that protocol was not subsequently pursued. When the ischaemia duration was reduced to 2 h and the DMTU dose to 400 mg/kg, a similar amelioration of the tissue damage was observed. However, since DMTU reduced a spontaneous rise in body temperature to 39.0-39.5 degrees C, DMTU-treated animals in the main series of experiments with 24 and 48 h of recovery were treated so that they had the same temperature rise as the saline controls. Under such constant temperature conditions, the effect of DMTU at 24 h of recovery was borderline (P = 0.052) and at 48 h it was nil. The lack of a lasting effect of DMTU was supported by the findings on evaluation of infarct area after 7 days of recovery. The results raise the important question whether DMTU, and perhaps other free radical scavengers, delay rather than ameliorate the ischaemic lesion developing after transient MCA occlusion.

Amelioration of retinal photic injury by a combination of flunarizine and dimethylthiourea

Free radical scavengers and a calcium overload blocker have been demonstrated separately to ameliorate light-induced retinal degeneration, suggesting that both free radical formation and increased intracellular calcium levels are involved in the pathologic changes of this disease process. To understand the relationship between these two mechanisms, we studied the ameliorative effects of combined treatment with flunarizine and dimethylthiourea as well as individual treatment with either drug in a rat model of light-induced retinal degeneration. At 6 hr and 6 and 14 days after light exposure, morphologic and morphometric studies of the retinas from the rats receiving the combined treatment demonstrated better-preserved retinal pigment epithelial cells, photoreceptor elements, and nuclei than did retinas from rats receiving treatment with either flunarizine or dimethylthiourea alone. Rhodopsin level measurements at 6 and 14 days further substantiated the results of the protective effects on the photoreceptor outer segments. Because we used a saturating dose for dimethylthiourea, the enhanced ameliorative effect of the combination treatment suggested that free radical formation and elevated intracellular calcium levels were two separate mechanisms in light-induced retinal degeneration.

Delayed onset and decreased incidence of diabetes in BB rats fed free radical scavengers

We tested the hypothesis that free radicals play a role in the selective destruction of pancreatic beta-cells in BB/Wor rats. Diabetes-prone BB rats of both sexes and 40 days of age were divided into three groups. The control group was fed ad libitum Purina rat chow powder, while the experimental group was fed ad libitum the rat chow powder blended with a mixture of four known free radical scavengers: allopurinol, mercaptopropionylglycine, dimethylthiourea and Vitamin E. A third group was pair-fed 10 g chow powder/rat/day, since in earlier experiments we observed that rats on the experimental diet consumed only about 10 g/rat/day. All rats were studied up to age 120 days. Body weight and food intake were measured daily. Urine was tested for glucose beginning at age 60 days. When glucosuria appeared, blood glucose and urinary ketones were measured. Body weight gain in the experimental and pair-fed groups was similar, but lower than the control group. Life table analysis of the data showed a decreased and a delayed onset of diabetes in the rats fed free radical scavengers. Thus, the results of this study demonstrated that calorie restriction and the related impaired growth did not affect the incidence of diabetes in the BB rat. In addition, the results suggested a role for free radicals in the spontaneous destruction of pancreatic beta-cells in the BB rat.

Dimethylthiourea ameliorates acute lung injury induced by phorbol myristate acetate in dogs

BACKGROUND AND METHODS

The protective effects of dimethylthiourea, a potent scavenger of hydroxy radical (.OH) and hydrogen peroxide, in experimental lung injury in large animals remain controversial. The present study was designed to determine whether dimethylthiourea can ameliorate the acute lung injury produced in dogs by phorbol myristate acetate. Six dogs were infused with dimethylthiourea (0.75 g/kg in saline) for 1.5 hrs, beginning 1 hr before an i.v. bolus injection of phorbol myristate acetate (17 micrograms/kg); six dogs received phorbol myristate acetate (17 micrograms/kg) alone; and six dogs were infused with saline alone. Hemodynamic changes, arterial oxygenation, and the development of lung edema were monitored for 4 hrs after phorbol myristate acetate injection to assess the extent of lung damage.

RESULTS

As compared with the dogs that received phorbol myristate acetate alone, the edematous lung damage was significantly reduced in those dogs that received dimethylthiourea as well as phorbol myristate acetate. In the dimethylthiourea-treated dogs, the lung wet/dry weight ratios were smaller (p less than .01); protein concentrations in lung lavage fluid were lower (p less than .01); the decrease in PaO2 was significantly reduced (p less than .01); and there were significant reductions in the alveolar-arterial oxygen tension difference (P[A-a]O2) (p less than .01) and shunt (Qsp/Qt) (p less than .05). Also, dimethylthiourea significantly lowered the increased mean pulmonary arterial pressure levels during the second half of the experiment.

CONCLUSIONS

These experimental data suggest that dimethylthiourea is capable of reducing the neutrophil-mediated lung injury produced by the release of hydroxy radical and/or hydrogen peroxide in dogs exposed to phorbol myristate acetate.

Protection by dimethylthiourea against retinal light damage in rats

The protective effect of dimethylthiourea (DMTU) against retinal light damage was determined in albino rats reared in darkness or in weak cyclic light. Rats maintained under these conditions were treated with DMTU at different concentrations and dosing schedules and then exposed for various times to intense visible light, either intermittently (1 hr light and 2 hr dark) or continuously. The extent of retinal light damage was determined 2 weeks after light exposure by comparing rhodopsin levels in experimental rats with those in unexposed control animals. To determine the effect of DMTU on rod outer segment (ROS) membrane fatty acids, ROS were isolated immediately after intermittent light exposure, and fatty acid compositions were measured. The time course for DMTU uptake and its distribution in serum, retina, and the retinal pigment epithelium (RPE)/choroid complex was determined in other rats not exposed to intense light. After intraperitoneal injection of the drug (500 mg/kg body weight), DMTU appeared rapidly in the serum, retina, and the RPE and choroid. In the ocular tissues, it was distributed 70-80% in the retina and 20-30% in the RPE and choroid. This antioxidant appears to have a long half-life because it was present in these same tissues 72 hr after a second intraperitoneal injection. For rats reared in the weak cyclic light environment, DMTU (two injections) provided complete protection against rhodopsin loss after intense light exposures of up to 16 hr. Only 15% rhodopsin loss was found in cyclic-light DMTU-treated rats after 24 hr of intermittent or continuous light. For rats reared in darkness, DMTU treatment resulted in a rhodopsin loss of less than 20% after 8-16 hr of continuous light and approximately 40% after similar exposure to intermittent light. Irrespective of the type of light exposure, rhodopsin loss in the dark-reared DMTU-treated rats was nearly identical to that found in uninjected cyclic light-reared animals. In rats from both light-rearing environments, DMTU treatment prevented the light-induced loss of docosahexaenoic acid from ROS membranes. As measured by rhodopsin levels 2 weeks later, DMTU was most effective when given as two doses administered 24 hr before and just before intense light exposure. As a single dose given during continuous light exposure, DMTU protected cyclic light-reared rats for at least 4 hr after the start of exposure but was ineffective in dark-reared animals if injected 1 hr after the start of light. It was also ineffective in both types of rats when given after light exposure.(ABSTRACT TRUNCATED AT 400 WORDS)