Pinealectomy and melatonin administration in rats: their effects on pulmonary edema induced by α-naphthylthiourea

We aimed to observe the possible effects of melatonin (MLT) deprivation (pinealectomy) and exogenous MLT administration on pulmonary edema induced by alpha-naphthylthiourea (ANTU), a toxic chemical agent, in rats. Seventy animals were assigned to seven groups: control, sham pinealectomy (PINX), PINX, ANTU (10 mg/kg intraperitoneal on day 30), ANTU + MLT (10 mg/kg/day i.p. for 30 days), ANTU + PINX, and ANTU + PINX + MLT.In this study, pleural effusion (PE) formation, lung weight/body weight (LW/BW) and PE/BW ratios (fluid accumulation and weight values in the lungs) increase detected. Pre-ANTU MLT administration led to significant decreases in PE, LW/BW, and PE/BW levels. The inhibited glutathione (GSH) and superoxide dismutase (SOD) levels and high malondialdehyde (MDA) levels that ANTU increase lipid peroxidation in the study. MLT administration eliminated oxidative stress by reducing MDA and ameliorating GSH and SOD levels.Pre-ANTU MLT administration led to a significant decrease in interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) levels in the lung when compared to the ANTU group without MLT administration. Post-pinealectomy ANTU administration significantly increased IL-1β and TNF-α levels when compared to ANTU and MLT administration without pinealectomy. Diffused inflammatory cell infiltration, interstitial pulmonary edema, and histopathological congestion were observed after the administration of ANTU. Severity of the damage was elevated in the ANTU + PINX group. MLT treatment regressed pulmonary effusion and edema and improves lung structure. In brief, the findings suggested that MLT inhibited proinflammatory mediators and could serve as a therapeutic agent to prevent inflammatory disorders.

Synthesis, acute toxicity, analgesic activity and cytotoxicity of Some bisthiourea derivatives

Bisthiourea derivatives were synthesized by the reaction of benzoylisothiocyanate and diamines to give 1,2-Bis(N'-benzoylthioureidobenzene (1), 1,3-di(benzoylthioureido)benzene (2) and 1,4-di(benzoylthioureido)benzene (3) in acetone. Acute toxicity study revealed that LD50 of compound (1) and (3) is 120 mg/kg body weight. Visceral pain induced by injecting i.p acetic acid in mice were strongly inhibited by all the compounds. 94.65, 95.25 and 85.54% analgesic activity were observed in compounds (1), (2) and (3) at 15 mg/kg and (2) and (3) shows 97.63 and 96.42% at 30 mg/kg body weight respectively while (1) gives 100% analgesic activity. 100% cytotoxicity was observed in compounds (2) and (3) and 96% in compound (1) at 750 ppm. The results suggest that these compounds may have potential values for treatment of cancer and painful disorders.

Synthesis, characterization, antioxidant and brine shrimp cytotoxic activity of novel 3-benzothioyl-1-(3-hydroxy-3-phenyl -3-propyl)-1-methylthiourea

In the present research work novel ephedrine based thiourea derivative, 3-benzothioyl-1-(3-hydroxy-3-phenyl -3-propyl)-1-methylthiourea 4is synthesized and then characterized elemental analyzed via various techniques i.e., Proton NMR, carbon13 NMR and fatherly confirmed via X-ray crystallography. Compound 4 was then screened for their possible antioxidant and cytotoxic potentials. Benzoyl chloride was treated with an equimolar potassium thiocyanate in acetone to achieve benzoyl isothiocyantes. It was then treated with an equimolar (1R, 2S)-(-)-Ephedrine to obtain the 3-benzothioyl-1-(3-hydroxy-3-phenyl-3-propyl)-1-methyl thiourea4. It was then screened for antioxidant and cytotoxic potentials. The compound 4 showed excellent antioxidant activity almost comparable to ascorbic acid (standard) and have significant cytotoxic activity with LC₅₀ value 05±0.58 ppm.

Moderate endoplasmic reticulum stress activates a PERK and p38-dependent apoptosis

The endoplasmic reticulum (ER) has the ability to signal organelle dysfunction via a complex signaling network known as the unfolded protein response (UPR). In this work, hamster fibroblast cells exhibiting moderate levels of ER stress were compared to those exhibiting severe ER stress. Inhibition of N-linked glycosylation was accomplished via a temperature-sensitive mutation in the Dad1 subunit of the oligosaccharyltransferase (OST) complex or by direct inhibition with tunicamycin (Tm). Temperature shift (TS) treatment generated weak activation of ER stress signaling when compared to doses of Tm that are typically used in ER stress studies (500-1000 nM). A dose-response analysis of key ER stress signaling mediators, inositol-requiring enzyme 1 (IRE1) and protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), revealed 20-40 nM of Tm to generate activation intensity similar to TS treatment. In parental BHK21 cells, moderate (20-40 nM) and high doses (200-1000 nM) of Tm were compared to identify physiological and signaling-based differences in stress response. Inhibition of ER Ca2+ release via ITPR activity with 2-aminoethoxydiphenyl borate (2-APB) or Xestospongin C (XeC) was sufficient to protect against apoptosis induced by moderate but not higher doses of Tm. Analysis of kinase activation over a range of Tm exposures revealed the p38 stress-activated protein kinase (SAPK) to display increasing activation with Tm dosage. Interestingly, Tm induced the extracellular regulated kinases (Erk1/2) only at moderate doses of Tm. Inhibition of ER transmembrane stress sensors (IRE1, PERK) or cytosolic signaling mediators (p38, Jnk1, Erk1/2) was used to evaluate pathways involved in apoptosis activation during ER stress. Inhibition of either PERK or p38 was sufficient to reduce cell death and apoptosis induced by moderate, but not high, doses of Tm. During ER stress, cells exhibited a rapid decline in anti-apoptotic Mcl-1 and survivin proteins. Inhibition of PERK was sufficient to block this affect. This work reveals moderate doses of ER stress to generate patterns of stress signaling that are distinct from higher doses and that apoptosis activation at moderate levels of stress are dependent upon PERK and p38 signaling. Studies exploring ER stress signaling should recognize that this signaling acts as a rheostat rather than a simple switch, behaving distinctively in a dose-dependent manner.

High Potency VEGFRs/MET/FMS Triple Blockade by TAS-115 Concomitantly Suppresses Tumor Progression and Bone Destruction in Tumor-Induced Bone Disease Model with Lung Carcinoma Cells

Approximately 25-40% of patients with lung cancer show bone metastasis. Bone modifying agents reduce skeletal-related events (SREs), but they do not significantly improve overall survival. Therefore, novel therapeutic approaches are urgently required. In this study, we investigated the anti-tumor effect of TAS-115, a VEGFRs and HGF receptor (MET)-targeted kinase inhibitor, in a tumor-induced bone disease model. A549-Luc-BM1 cells, an osteo-tropic clone of luciferase-transfected A549 human lung adenocarcinoma cells (A549-Luc), produced aggressive bone destruction associated with tumor progression after intra-tibial (IT) implantation into mice. TAS-115 significantly reduced IT tumor growth and bone destruction. Histopathological analysis showed a decrease in tumor vessels after TAS-115 treatment, which might be mediated through VEGFRs inhibition. Furthermore, the number of osteoclasts surrounding the tumor was decreased after TAS-115 treatment. In vitro studies demonstrated that TAS-115 inhibited HGF-, VEGF-, and macrophage-colony stimulating factor (M-CSF)-induced signaling pathways in osteoclasts. Moreover, TAS-115 inhibited Feline McDonough Sarcoma oncogene (FMS) kinase, as well as M-CSF and receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation. Thus, VEGFRs/MET/FMS-triple inhibition in osteoclasts might contribute to the potent efficacy of TAS-115. The fact that concomitant dosing of sunitinib (VEGFRs/FMS inhibition) with crizotinib (MET inhibition) exerted comparable inhibitory efficacy for bone destruction to TAS-115 also supports this notion. In conclusion, TAS-115 inhibited tumor growth via VEGFR-kinase blockade, and also suppressed bone destruction possibly through VEGFRs/MET/FMS-kinase inhibition, which resulted in potent efficacy of TAS-115 in an A549-Luc-BM1 bone disease model. Thus, TAS-115 shows promise as a novel therapy for lung cancer patients with bone metastasis.

A Study of the Potential of the Pig as a Model for the Vaginal Irritancy of Benzalkonium Chloride in Comparison to the Nonirritant Microbicide PHI-443 and the Spermicide Vanadocene Dithiocarbamate

A porcine model was established to test the mucosal toxicity potential of a thiophene thiourea (PHI-443)-based anti-HIV microbicide and a vanadocene-based spermicide, vanadocene dithiocarbamate (VDDTC) in comparison to benzalkonium chloride (BZK). Nine domestic pigs (Duroc) in nonestrus stage received a single intravaginal application of 2% BZK, 2% PHI-443, or 0.1% VDDTC-containing gel. At various times after gel application, cell differentials and levels of inflammatory cytokines (IL-1 β, IL-4, IL-6, IL-8, IL-10, IL-18, IFN- γ, and TNF- α) in cervicovaginal lavage (CVL) fluid were monitored by flow cytometry and ELISA, respectively. Eight pigs were exposed intravaginally to a gel with and without BZK or VDDTC for 4 consecutive days and vaginal tissues were scored histologically for inflammation using a new scoring system. Only CVL fluid from pigs exposed to BZK showed a significant increase of IL-1 β, IL-8, and also IL-18 production when compared to the controls, PHI-443 or VDDTC-treated groups. Maximum levels of BZK-induced IL-1 β (100-fold), IL-8 (2,500-fold), IL-18 (80-fold), and IFN- γ(10-fold) were found at 24 hours. In the in vivo porcine vaginal irritation model, increased levels of vaginal IL-1 β, IL-8, and IL-18 were associated with histological changes consistent with vaginal inflammation. These results demonstrate that key cervicovaginal inflammatory cytokines are useful in vivo biomarkers for predicting the mucosal toxicity potential of vaginal products in the physiologically relevant and sensitive porcine model.

[Effect of carcinogenic nitrogen-containing compounds on cell metabolism]

The brown frog (Rana temporaria) skin cells respiration, calcium metabolism and glycolysis, the tree frog (Hyla arborea) skin cells respiration and calcium metabolism were studied under short-term (first hours) and long-term (first days) exposure to nitrogenous compounds [N-nitroso-N-methyl urea (NMU) and thiourea (TU)]. The first direct effect of nitrogenous compounds exposure was cell breathing inhibition occurring in Rana temporaria skin cells after 28 days of exposure, and in Hyla arborea skin cells after 8 days of exposure. These changes were precided by decrease of lactate dehydrogenase (LDH) activity in Rana temporaria skin cells starting 16 days after NMU and TU introduction. The increase of intracellular calcium level was noted in tree frog skin cells 4-8 days after NMU and TU introduction, in brown frogs skin cells this parameter was unchanged.

[Allergic contact dermatitis to diethylthiourea in a neoprene wader]

Diethylthiourea, like other thioureas, is often used by the rubber industry and in the manufacture of neoprene. We present a patient who suffered allergic contact dermatitis to diethylthiourea in a neoprene wader and who required admission to hospital and systemic treatment. We review the literature on allergy to diethylthiourea. Thioureas are not included in the standard GEIDAC (Spanish Contact Dermatitis Research Group) battery of patch tests. In these cases, it is necessary to use a special battery of rubber allergens, which includes thiourea compounds, for diagnosis of the disease and to ensure that cases of contact allergic dermatitis to thioureas do not go undiagnosed.

Uptake–toxicity relationships of a series of N-substituted N′-(4-imidazole-ethyl)thiourea in precision-cut rat liver slices

A previous study showed that the cytotoxicity of a series of N-p-phenyl-substituted N'-(4-imidazole-ethyl)thiourea in precision-cut rat liver slices increased with increasing electron-withdrawing capacity of the p-substituent and may be related to the Vmax/Km values of bioactivation of the thiourea-moiety by hepatic flavin-containing monooxygenases (FMOs). However, differences in the uptake of xenobiotics into precision-cut liver slices can also have consequences for the rates of metabolism of xenobiotics. In the present study, therefore, we investigated the rate and nature of uptake of 9 N-substituted N'-(4-imidazole-ethyl)thiourea into precision-cut rat liver slices. It was found that a five-fold difference exists among a series of N-substituted N'-(4-imidazole-ethyl)thiourea both in the initial rate of uptake and in the steady-state levels ultimately achieved in the precision-cut rat liver slices. It appeared that the most cytotoxic compounds were also the most readily absorbed compounds. The concentration-dependent initial rate of uptake could be described by a carrier-mediated saturable component and a non-saturable component. At cytotoxic concentrations, the non-saturable component accounted for more than 95% of the total uptake. From this study, it is concluded that differences in rate of uptake of thiourea-containing compounds may be a contributing factor to the differences in bioactivation by FMOs as the basis of the structure-toxicity relationships observed in precision-cut rat liver slices.

Defective fin regeneration in medaka fish (Oryzias latipes) with hypothyroidism

Wild-type medaka are known to have remarkable capabilities of fin, or epimorphic, regeneration. However, a hypothyroid mutant, kamaitachi (kmi), frequently suffers from injury in fins, suggesting an important role of thyroid hormone in fin regeneration. This led us to examine the relationship between thyroid hormone and fin regeneration using medaka as a model. For this, we first set up a medaka experimental system in which the rate of regeneration was statistically analyzed after caudal fin amputation under normal and hypothyroid conditions. As expected, the regeneration of amputated caudal fins was delayed in hypothyroid kmi -/- mutants. We then examined wild-type medaka with thiourea-induced hypothyroidism to evaluate the requirement of thyroid hormone during epimorphic fin regeneration. The results demonstrate that the growth rate of regenerates was much reduced in severely hypothyroid medaka throughout the regeneration period. This reduction in regenerative rate was recovered by exogenous administration of L-thyroxine. The present study is thus the first to report the direct involvement of thyroid hormone in teleost fin regeneration, and provides a basic framework for future molecular and genetic analyses.

A synchronized amphibian metamorphosis assay as an improved tool to detect thyroid hormone disturbance by endocrine disruptors and apolar sediment extracts

Amphibian metamorphosis assays are used to evaluate potential effects of endocrine disrupting compounds on the thyroid hormone axis. In this study, Xenopus laevis tadpoles are kept in a solution of 0.2% thiourea (TU) to arrest and synchronise them in their development. The advantage of this synchronized amphibian metamorphosis assays is that synchronised tadpoles are available at any time to start metamorphosis experiments, and experimental groups are much more homogenous at the start of experimental exposure compared with groups selected from an untreated pool of animals. The water volume per animal was kept constant throughout the experimental period to overcome the influence of declining numbers of animals per aquarium due to metamorphosis and mortality on the density dependent development of the remaining tadpoles. Clophen A50 (a technical PCB mixture), the single congener 3,3',4,4'-tetrachlorobiphenyl (PCB 77) and apolar sediment extracts that were previously tested positive in the T-Screen, an in vitro proliferation assay for thyroid hormone disruption, were tested in the Synchronized Amphibian Metamorphosis Assay. Endpoints studied were mortality, malformations, body weight, and percentage of metamorphosed froglets at the end of the 60-day experimental period, percentage of tadpoles in different developmental stages, and developmental stage-dependent awarded penalty points. Dietary exposure to Clophen A50 (0.2-50mg/kg food) resulted in a significant increased percentage of tadpoles that did not pass metamorphosis at concentrations higher than 2mg/kg food. Time until metamorphosis in those animals that were able to metamorphose after the 60-days experimental period was significantly decreased. Dietary exposure to PCB 77, a congener that can be readily metabolised, did not result in significant effects in any exposure group (2-500 microg/kg food). Apolar sediment extracts from two of the three sites that are contaminated with a wide variety of chemicals significantly decreased the percentage of metamorphosed animals and significantly increased the number of tadpoles that remained in early and late metamorphic stages. These effects already occurred when the extracts where diluted more than 1000 times (on an organic carbon base) compared to environmental concentrations. The rank of potency was comparable to results obtained with the T-screen. This suggests the presence of thyroid hormone disrupting compounds in the aquatic environment and possible effects of such compounds on animal development in the wild.

In vivo pharmacokinetics and toxicity of a novel hydrophilic oral formulation of the potent non-nucleoside reverse transcriptase inhibitor compound N'-[2-(2-thiophene)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (HI-443)

The thiophene ethyl thiourea (TET) compound N'-[2-(2-thiophene)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (HI-443) is a potent non-nucleoside reverse transcriptase inhibitor (NNRTI). The pharmacokinetics of 17 different novel oral formulations of HI-443 were compared in an attempt to identify the most suitable dosage form for clinical use in HIV-infected persons. Plasma concentrations of HI-443 were monitored in mice after administration of the drug using these 17 different formulations at three time points. Two-way ANOVA showed highly significant formulation (p < 0.0001), time (p < 0.0001) and formulation*time interaction effects (p = 0.0003). Planned linear contrasts were performed to identify which formulations showed the highest bioavailability at 10, 30, 60 min and at all time points relative to DMSO alone. A significant positive regression was observed comparing bioavailibility of HI-443 at 10 min and hydrophilic-lipophilic balance (HLB) values of the formulations (R2 = 26%, p < 0.0001). The results showed that formulations that were hydrophilic, containing PEG400 and propylene glycol, gave the highest overall drug concentrations over the 60-min time period. The lead oral formulation of HI-443 exhibited a very favorable toxicity profile in BALB/c mice.

Improved oral bioavailability of anti-HIV agent N'-[2-(2-thiophene)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (HI-443) in a novel lipophilic formulation

N'-[2-(2-Thiophene)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (CAS 258340-15-7, HI-443) is a rationally designed non-nucleoside reverse transcriptase inhibitor (NNRTI) with potent anti-HIV activity at nanomolar concentrations but poor oral bioavailability. Here the identification of a novel oleic acid containing lead formulation of HI-443 is described which resulted in a approximately 10-fold improvement of its oral bioavailability yielding 10-fold higher systemic exposure levels in mice. Formulated HI-443 exhibited a favorable pharmacokinetics and toxicity profile in mice.

Antimycobacterial activity of novel 1-(5-cyclobutyl-1,3-oxazol-2-yl)-3-(sub)phenyl/pyridylthiourea compounds endowed with high activity toward multidrug-resistant Mycobacterium tuberculosis

OBJECTIVES

The objective of this work was to synthesize 15 new 1-(5-cyclobutyl-1,3-oxazol-2-yl)-3-(sub)phenyl/pyridylthiourea compounds and evaluate their in vitro and in vivo antimycobacterial activities.

METHODS

5-Cyclobutyloxazol-2-amine was reacted with 1,1'-thiocarbonyldiimidazole, followed by various substituted anilines and 2-amino pyridines to yield the 15 compounds, which were subjected to in vitro and in vivo evaluation against Mycobacterium tuberculosis H37Rv (MTB) and a clinical isolate of multidrug-resistant M. tuberculosis (MDR-TB).

RESULTS

Among the 15 compounds screened, 7 compounds inhibited both MTB and MDR-TB in vitro with MICs of < 1 microM. In the in vivo screening, compound 1-(5-cyclobutyl-1,3-oxazol-2-yl)-3-(2'-trifluoromethyl)phenylthiourea (compound 8) was equally active as isoniazid at the same dose level.

CONCLUSIONS

Compound 8 was found to be the most active, with an in vitro MIC of 0.14 microM and was 2.5 and 80 times more active than isoniazid against MTB and MDR-TB, respectively. Compound 8 was non-toxic to Vero cells up to 183 microM, with a selectivity index of > 1307. In the in vivo animal model, compound 8 decreased the mycobacterium load in lung and spleen tissues with 2.8 and 3.94 log(10) reductions, respectively.

In vivo pharmacokinetics, metabolism, toxicity, and anti-HIV activity of N'-[2-(2-Thiophene)ethyl]-N'-[2-(5-bromopyridyl)]thiourea (HI-443), a potent non-nucleoside inhibitor of HIV reverse transcriptase

N'-[2-(2-Thiophene)ethyl]-N'-[2-(5bromopyridyl)]thiourea (CAS 258340-15-7, HI-443) is a potent non-nucleoside inhibitor of HIV reverse transcriptase (NNRTI) that was rationally designed as a candidate anti-HIV agent. The purpose of the present study was to examine the in vivo pharmacokinetics, metabolism, toxicity, and anti-HIV activity of HI-443. HI-443 was very well tolerated in CD-1 mice and Lewis rats without any detectable toxicity at single parenteral bolus dose levels as high as 80 mg/kg. Intraperitoneally administered HI-443 exhibited anti-HIV activity in the Hu-PBL-SCID mouse surrogate model for hunnan AIDS at a non-toxic daily dose level of 10-20 mg/kg. These preclinical research studies provide the basis for future preclinical studies and clinical development of HI-443 as a new NNRTI candidate.

DNA fragmentation and DNA repair synthesis induced in rat and human thyroid cells by chemicals carcinogenic to the rat thyroid

Five chemicals that are known to induce in rats thyroid follicular-cell adenomas and carcinomas were assayed for their ability to induce DNA damage and DNA repair synthesis in primary cultures of human thyroid cells. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the same Comet assay, were obtained after a 20-h exposure to the following subtoxic concentrations of the five test compounds: methimazole from 2.5 to 10mM; nitrobenzene, potassium bromate, N,N'-diethylthiourea and ethylenethiourea from 1.25 to 5mM. Under the same experimental conditions, DNA repair synthesis, as evaluated by quantitative autoradiography, was present in potassium bromate-exposed thyroid cells from all the three donors and in those from two of three donors with either nitrobenzene or ethylenethiourea, but did not match the criteria for a positive response in thyroid cells from any of the donors with methimazole and N,N'-diethylthiourea. Consistently with their ability to induce thyroid tumors, all the five test compounds, administered p.o. in rats in a single dose corresponding to 1/2 LD50, induced a statistically significant degree of DNA fragmentation in the thyroid. These findings suggest that the five test compounds might be carcinogenic to thyroid in humans.

Genotoxicity of dental resin polymerization initiators in vitro

The polymerization initiators for resins cured using visible light usually consist of a photosensitizer, primarily camphorquinone (CQ), and a reducing agent, which is often a tertiary amine (DMPT, DMAEMA), while the initiator used for self-curing resins consists of benzoyl peroxide (BPO) and a tertiary amine (DMPT). The genotoxicities of camphorquinone (CQ), benzoyl peroxide (BPO), dimethyl-para-toluidine (DMPT), 2-dimethylamino-ethyl-methacrylate (DMAEMA), and 1-allyl-2-thiourea (ATU) were examined using the bioluminescent bacterial genotoxicity test. 4-Nitroquinoline-N-oxide (4NQO) was prepared for comparison with these chemicals. Acetone solutions of the five polymerization initiators and 4NQO were prepared. Benzoyl peroxide (BPO), dimethyl-para-toluidine (DMPT), and 1-allyl-2-thiourea (ATU) showed significant genotoxic activity at 24 h in the bioluminescent bacterial genotoxicity test, at concentrations of approximately 5 microM, 4 mM, and 1 mM, respectively. 2-Dimethyloamino-ethyl-methacrylate (DMAEMA) did not have genotoxic activity and CQ had questionable genotoxic activity. In comparison, 4NQO had strong genotoxicity, at 4 microM, roughly the same as that of BPO. Therefore, BPO should be used carefully in clinical dentistry.

Studies on the goitrogenic mechanism of action of N,N,N',N'-tetramethylthiourea

N,N,N',N'-Tetramethylthiourea (TMTU) is a rat goitrogen inducing thyroid hyperplasia, hypertrophy, and tumor formation. Little is known about the exact underlying mechanism of action. As thyroid peroxidase (TPO) and type I iodothyronine deiodinase (ID-I) have been established as targets of goitrogenic thiourea derivatives, we investigated interactions of TMTU with target enzymes using a partially purified fraction from hog thyroids or solubilized hog thyroid microsomes and 10,000g supernatant from rat liver homogenate, respectively, as enzyme sources. For comparison, comprehensively characterized goitrogenic thiourea derivatives were studied as well. In contrast to propylthiouracil (PTU), and like ethylenethiourea (ETU), TMTU only marginally affected TPO-catalyzed oxidation of guaiacol. TMTU, like ETU, concentration-dependently suppressed TPO-catalyzed iodine formation with concomitant oxidative metabolism. Suppression ceased upon consumption of thiourea derivatives, the rate of the reappearing iodine formation was similar to that of controls. TMTU, like ETU, also suppressed non-enzymatic and TPO-catalyzed monoiodination of l-tyrosine with a stoichiometry of 2:1, i.e., one molecule of thiourea derivative suppressed two times monoiodination. TMTU and ETU were unable to irreversibly inhibit TPO. In contrast to PTU, TMTU did not inhibit ID-I. These findings provide evidence that TMTU interferes with thyroid hormone synthesis at the level of iodination and demonstrate a metabolic route for the oxidative detoxification of TMTU in the thyroid suggesting that low-level or intermittent exposure to TMTU would have only minimal effects on thyroid hormone synthesis. Finally, it can be concluded that meaningful toxicological studies on TPO inhibition can be performed without a need for highly purified TPO.

Oxidized low-density lipoproteins accumulate in rat lung after experimental lung edema induced by alpha- naphthylthiourea (ANTU)

Oxidation of the low-density lipoprotein (LDL) results in the production of modified LDLs. Oxidation of LDL cholesterol plays a role on the pathogenesis of endothelial dysfunction. This study was designed to investigate the possible participation of the oxidative modification of low density lipoprotein in the lung edema induced by alpha-naphthylthiourea (ANTU), which is a well-known noxious chemical agent on the lung endothelium. When ANTU injected intraperitoneally into rats (15 mg kg(-1)), it produced lung edema as indicated by an increase in lung weight/body weight (LW/BW) ratio and pleural effusion (PE) reaching a maximum within 4 h. A significant lung edema was observed 4 h after intraperitoneally injection of alpha-naphthylthiourea when compared with olive oil-injected control rats. On microscopic examination of alpha-naphthylthiourea-treated rats were shown to have severe lung injury, while no change was observed in olive oil-treated control rats. While there were no staining in control lungs, positive oxidized low-density lipoproteins immune-fluorescent staining were observed in lung edema group. Our study showed that oxidized low-density lipoprotein (oxLDL) accumulated in ANTU-induced lung damage. This is the first study in which accumulation of oxLDL molecules in the intact lung tissue were shown by fluorescent immune-staining method in experimental lung edema. The potential role of oxLDL in this pathology are still under investigation.

Morphine modulates inducible nitric oxide synthase expression and reduces pulmonary oedema induced by α-naphthylthiourea

This study was designed to investigate the possible participation of morphine in pulmonary oedema induced by alpha-naphthylthiourea (ANTU), which is a well-known noxious chemical agent in the lung. Injection of ANTU (15 mg/kg i.p.) produced pulmonary oedema as indicated by an increase in lung weight/body weight ratio and pleural effusion reaching a maximum within 4 h in rat. Administration of morphine prior to ANTU significantly inhibited to pulmonary oedema with a dose-dependent manner. The protective effect of morphine is prevented by peripheral opioid receptor antagonist, naloxone methiodide. ANTU-treated rats were shown positive by inducible nitric oxide synthase immunohistochemical staining. There was no staining in the control group. On the other hand, the degree of staining was markedly reduced in tissue sections by morphine. These results suggest that previous administration of subcutaneous morphine has preventive effect on ANTU-induced pulmonary inflammatory reaction and its effect mediated via peripheral opioid receptors. Application of naloxone with ANTU has no effect on the lung parameters indicating that endogenous opioids do not modulate ANTU-induced damage.

A Selective Inhibitor of eIF2 Dephosphorylation Protects Cells from ER Stress

Most protein phosphatases have little intrinsic substrate specificity, making selective pharmacological inhibition of specific dephosphorylation reactions a challenging problem. In a screen for small molecules that protect cells from endoplasmic reticulum (ER) stress, we identified salubrinal, a selective inhibitor of cellular complexes that dephosphorylate eukaryotic translation initiation factor 2 subunit alpha (eIF2alpha). Salubrinal also blocks eIF2alpha dephosphorylation mediated by a herpes simplex virus protein and inhibits viral replication. These results suggest that selective chemical inhibitors of eIF2alpha dephosphorylation may be useful in diseases involving ER stress or viral infection. More broadly, salubrinal demonstrates the feasibility of selective pharmacological targeting of cellular dephosphorylation events.

Comparative cytotoxicity of N-substituted N′-(4-imidazole-ethyl)thiourea in precision-cut rat liver slices

In order to more rationally design thiourea-containing drugs and drug candidates, specifically thiourea-containing histamine H3 receptor antagonists, it is necessary to develop structure-toxicity relationships (STRs). For this purpose, the cytotoxicity of a series of thiourea-containing compounds was tested in precision-cut rat liver slices. A concentration of 1000 microM of N-p-bromophenyl, N'-(4-imidazole-ethyl)thiourea (8) or N-p-nitrophenyl, N'-(4-imidazole-ethyl)thiourea (9) was found to cause cytotoxicity, evidenced as LDH leakage, resulting in more than 95% LDH leakage after 6h. N-p-Methoxyphenyl, N'-(4-imidazole-ethyl)thiourea (6) caused 40.6 +/- 19.7% LDH leakage after 6h. Control levels of cell death (1% methanol as control vehicle) were below 20% in 6h. After 6h of exposure, N-p-chlorophenyl, N'-(4-imidazole-ethyl)thiourea (7), 8, and 9 were already found to cause significant cytotoxicity at a concentration of 100 microM. At 200 microM, 9 was found to cause significantly more cytotoxicity than 7 and 8. N-Naphthyl, N'-(4-imidazole-ethyl)thiourea (12) was found to cause significant cytotoxicity towards precision-cut rat liver slices after 6h of exposure to a concentration of 500 microM. All other N-substituted, N'-(4-imidazole-ethyl)thiourea tested in this study were not found to be cytotoxic towards precision-cut rat liver slices within the 6h of exposure up to a concentration of 1000 microM. Intracellular glutathione (GSH) content and mitochondrial MTT reduction activity were also examined after exposure of slices to N-substituted, N'-(4-imidazole-ethyl)thiourea. Both of these markers, however, were not found to provide additional information regarding the possible mechanisms of cytotoxicity, i.e. GSH depletion or reduced mitochondrial activity since these markers did not clearly precede LDH leakage. A correlation was found between cytotoxicity towards precision-cut rat liver slices and Vmax/Km values for the formation of sulfenic acids from N-substituted N'-(4-imidazole-ethyl)thiourea by hepatic rat flavin-containing monooxygenases (FMO). The compound with the highest Vmax/Km value for the formation of sulfenic acids, 9, was also the most cytotoxic. Compounds with a significantly lower Vmax/Km value, 7, 8, and 12, were less cytotoxic than 9. Compounds with a Vmax/Km value for the formation of sulfenic acids lower than 0.0788 ml/(minmg) were found not to be cytotoxic towards precision-cut rat liver slices for concentrations up to 1000 microM at an exposure time of 6h. It is concluded, from this study, that N-phenyl substituted N'-(4-imidazole-ethyl)thiourea-containing electron-withdrawing p-substituents are cytotoxic towards precision-cut rat liver slices. Cytotoxicity is increased with increasing electron-withdrawing capacity of the p-substituent. A correlation was found to exist between Vmax/Km value for the formation of sulfenic acids by rat liver FMO enzymes and cytotoxicity.

Effects of TNFalpha on expression of ICAM-1 in human airway epithelial cells in vitro: oxidant-mediated pathways and transcription factors

We demonstrate that two different cell-permeable antioxidants, pyrrolidine dithiocarbamate (PDTC) and dimethylthiourea (DMTU), inhibit TNFalpha-induced ICAM-1 surface and gene expression in primary cultures of differentiated normal human bronchial epithelial (NHBE) cells. In addition, TNFalpha stimulates binding of nuclear proteins to the nuclear factor kappa beta (NFkappaB) and the CAAT/enhancer binding protein (C/EBP) consensus sites in the ICAM-1 promoter in these cells. Because these transcription factors have been suggested to be oxidant-sensitive and important in ICAM-1 expression, the potential involvement of reactive oxygen species (ROS) in the response to TNFalpha was investigated. Interestingly, neither PDTC nor DMTU altered binding of NFkappaB complexes. In contrast, either the proteasome inhibitor carbobenzoxy-L-leucy-L-leucy-L-leucinal (MG 132) or the IkappaBalpha inhibitor BAY 11-7082 ablated TNFalpha-induced ICAM-1 gene expression and MG132 inhibited TNFalpha-induced NFkappaB complexes. Surprisingly, either PDTC or DMTU inhibited the binding of TNFalpha-enhanced C/EBP complexes to the consensus site directly adjacent to the NFkappaB site. These results suggest that although TNFalpha enhances binding of C/EBP and NFkappaB complexes in NHBE cells, C/EBP binding seems to involve an oxidant-dependent mechanism, whereas activation of NFkappaB complexes utilizes the ubiquitin-proteasome pathway, a mechanism that seems to be unaltered by the presence of antioxidants. Because interference with either signaling pathway abrogates TNFalpha-induced ICAM-1 expression, activation of both complexes seems to be involved in this response to TNFalpha, but this activation occurs via different intracellular pathways.

Carcinogenic effect of combined administration of 2,4-diaminoanisole sulfate, 4,4'-thiodianiline and N,N'-diethylthiourea in male Wistar rats

Male Wistar rats were divided into two groups. Rats of group 1 were fed basal powdered diet containing 610 ppm 2,4- diaminoanisole sulfate (DAAS), 46 ppm 4,4'-thiodianiline (TDA) and 200 ppm N,N'-diethylthiourea (DETU) for 52 weeks (DTD treatment). Rats of group 2 were maintained on basal diet throughout the experiment as controls. At 52 weeks all surviving rats were sacrificed and subjected to an autopsy. Thyroid, lungs, stomach, liver, spleen, kidneys, testes and all gross lesions suspected of being a tumor were removed. After DTD treatment, the incidence of thyroid hyperplasia and papillary thyroid carcinoma was 59% (10/17) and 65% (11/17), respectively. Hepatocellular adenoma was induced in 2 of 17 rats (12%). Papillary thyroid carcinoma metastasis was found in the lung of 1 rat. No neoplastic tumors were found in kidney, spleen, stomach and testis tissue.

Hypothalamic gene expression in reproductively photoresponsive and photorefractory Siberian hamsters

An interval timing mechanism in the brain governs reproduction in seasonally breeding mammals by triggering refractoriness to inhibitory short photoperiods during midwinter. The neural mechanisms responsible for the timing and induction of photorefractoriness by this seasonal clock are unknown. Using cDNA microarrays and RT-PCR, we identified a class of genes encoding thyroxine (T4)-binding proteins (transthyretin, T4-binding globulin, albumin) whose expression is associated with reproductive refractoriness to short day lengths. Down-regulation of these genes was associated with reduced hypothalamic T4 uptake, which was reversed by long-day photoperiod treatments that restored responsiveness to short days. Circulating T4 concentrations did not vary with states of photoresponsiveness in euthyroid hamsters, but blockade of thyroid function accelerated the onset of photorefractoriness to short days. These data link changes in gene expression in the hypothalamus to the functional output of a seasonal clock. Reproductive inhibition in short days depends on T4 only late in the nonbreeding season. Down-regulation of genes encoding T4-binding proteins in the hypothalamus during this interval may restrict access of a static T4 signal to hypothalamic target tissues that regulate reproduction, thereby timing annual transitions in reproductive function. Hypothalamic autoregulation of T4 influx may constitute a critical cellular process involved in the generation and expression of seasonal reproductive rhythms and suggests a previously undescribed mechanism by which neural targets gain access to peripheral hormones.

A 13-week subchronic intravaginal toxicity study of the novel broad-spectrum anti-HIV and spermicidal agent, N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (PHI-346) in mice

The nonnucleoside inhibitor (NNI) of HIV-1 reverse transcriptase, PHI-346 (N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea), is a dual-function spermicidal agent with potent anti-HIV activity against drug-sensitive as well as drug-resistant HIV-1 strains with genotypic and phenotypic NNI resistance. PHI-346 was formulated via a lipophilic gel-microemulsion for intravaginal use as a potential dual-function microbicide. To evaluate the toxicity potential of short-term intravaginal exposure to PHI-346, groups of 15 female B6C3F1 and CD-1 mice were exposed intravaginally to a gel-microemulsion containing 0, 0.5, 1.0, or 2.0% PHI-346, 5 days per week for 13 consecutive weeks. On a molar basis, these concentrations of PHI-346 are 350 to 1,400-times higher than its spermicidal EC50 and nearly 5 x 10(6) to 2 x 10(7) times higher than its in vitro anti-HIV IC50. After 13 weeks of intravaginal treatment, B6C3F1 mice were evaluated for survival, body weight gain, absolute and relative organ weights. Blood was analyzed for hematology and clinical chemistry profiles. Microscopic examination was performed on hematoxylin and eosin-stained tissue sections from each study animal. Placebo control and PHI-346 dosed female CD-1 mice were mated with untreated males in order to evaluate if PHI-346 has any deleterious effects on the reproductive performance. There were no treatment-related mortalities. Mean body weight gain during the dosing period was not reduced by PHI-346 treatment. The hemogram or blood chemistry profiles revealed lack of systemic toxicity following daily intravaginal instillation of PHI-346 for 13 weeks. No clinically significant changes in absolute and relative organ weights were noted in PHI-346 dose groups. Extensive histopathological examination of tissues revealed no treatment-related abnormalities in any of the three PHI-346 dose groups. Repeated intravaginal exposure of CD-1 mice to increasing concentrations of PHI-346 for 13 weeks had no adverse effect on their subsequent reproductive capability, perinatal outcome, growth, and development of offspring. Collectively, these findings demonstrate that repetitive intravaginal administration of PHI-346 at concentrations as high as 1,400-times its spermicidal EC50 and 2 x 10(7) times its in vitro anti-HIV IC50 was not associated with local or systemic toxicity and did not adversely affect the reproductive performance in mice. PHI-346 may be useful as an active ingredient of a safe vaginal microbicide for prevention of the sexual transmission of multidrug-resistant HIV-1.

Exacerbation by granulocyte colony-stimulating factor of prior acute lung injury: implication of neutrophils

OBJECTIVE

Granulocyte colony-stimulating factor is widely prescribed to hasten recovery from cancer chemotherapy-induced neutropenia and has been reported to induce pulmonary toxicity. However, circumstances and mechanisms of this toxicity remain poorly known.

DESIGN

To reproduce a routine situation in cancer patients receiving chemotherapy, we investigated the mechanisms underlying granulocyte colony-stimulating factor-induced exacerbation of alpha-naphthylthiourea-related pulmonary edema.

SETTING

Laboratory research unit.

SUBJECTS

Male specific-pathogen-free Sprague-Dawley rats.

INTERVENTIONS

The effects of granulocyte colony-stimulating factor given alone or after alpha-naphthylthiourea used to induce acute lung injury were investigated.

MEASUREMENTS AND MAIN RESULTS

Lung injury was assessed based on neutrophil sequestration (myeloperoxidase activity in lung tissue) and influx into alveolar spaces (bronchoalveolar lavage fluid cell quantification) and on edema formation (wet/dry lung weight ratio) and alveolar protein concentration into bronchoalveolar lavage fluid. Tumor necrosis factor-alpha and interleukin-1beta were measured in serum, lung homogenates, and isolated alveolar macrophage supernatants. In control rats, granulocyte colony-stimulating factor (25 microg/kg) significantly elevated circulating neutrophil counts without producing alveolar recruitment or pulmonary edema. alpha-Naphthylthiourea significantly increased the wet/dry lung weight ratio (4.68 +/- 0.04 vs. 4.38 +/- 0.07 in controls, p=.04) and induced alveolar protein leakage. Adding granulocyte colony-stimulating factor to alpha-naphthylthiourea exacerbated pulmonary edema, causing neutrophil sequestration in pulmonary vessels, significantly increasing lung myeloperoxidase activity (12.7 +/- 2.0 mOD/min/g vs. 1.1 +/- 0.4 mOD/min/g with alpha-naphthylthiourea alone; p<.0001), and increasing proinflammatory cytokine secretion. alpha-Naphthylthiourea-related pulmonary edema was not exacerbated by granulocyte colony-stimulating factor during cyclophosphamide-induced neutropenia or after lidocaine, which antagonizes neutrophil adhesion to endothelial cells. Tumor necrosis factor-alpha and interleukin-1beta concentrations in alveolar macrophage supernatants and lung homogenates were significantly higher with alpha-naphthylthiourea + granulocyte colony-stimulating factor than with either agent alone, and anti-tumor necrosis factor-alpha antibodies abolished granulocyte colony-stimulating factor-related exacerbation of alpha-naphthylthiourea-induced pulmonary edema. In rats with cyclophosphamide-induced neutropenia, tumor necrosis factor-alpha concentrations in alveolar macrophage supernatants and lung homogenates were significantly decreased compared with rats without neutropenia.

CONCLUSION

Granulocyte colony-stimulating factor-related pulmonary toxicity may involve migration of neutrophils to vascular spaces, adhesion of neutrophils to previously injured endothelial cells, and potentiation of proinflammatory cytokine expression.

Effects of the dithiocarbamate fungicide propineb in primary neuronal cell cultures and skeletal muscle cells of the rat

After repeated-dose toxicity studies with the fungicide propineb, reversible effects on muscle functions were found. Therefore, mechanistic investigations should contribute to clarification of its mode of action in relation to disulfiram and diethyldithiocarbamate neurotoxicity or direct effects on muscle cells. In principle, besides the dithiocarbamate effects, two different mechanisms have been discussed for this fungicide. One mechanism is the degradation to carbon disulfide (CS(2)) and propylenthiourea (PTU) and the other are direct effects of zinc. Primary neuronal cell cultures of the rat are a well established model to identify neurotoxic compounds like n-hexane or acrylamide. In this cell culture model, endpoints such as viability, energy supply, glucose consumption and cytoskeleton elements were determined. Additionally, skeletal muscle cells were used for comparison. Propineb and its metabolite PTU were investigated in comparison to CS(2), disulfiram and diethyldithiocarbamate. The toxicity of zinc was tested using zinc chloride (ZnCl(2)). It was clearly shown that propineb exerted strong effects on the cytoskeleton of neuronal and non-neuronal cell cultures (astrocytes, muscle cells). This was similar to ZnCl(2,) but not to CS(2). With CS(2) and disulfiram effects on the energy supply were more prominent. In conclusion, the toxicity of propineb is not comparable to disulfiram, diethyldithiocarbamate or CS(2) neurotoxicity. In regard to these findings, a direct reversible effect of propineb on skeletal muscle cells seems to be more likely.

Thiourea toxicity in mouse C3H/10T1/2 cells expressing human flavin-dependent monooxygenase 3

Human flavin-dependent monooxygenase (FMO) isoforms 1 and 3 were expressed by retroviral gene transfer in mouse C3H/10T1/2 cells. FMO function was determined by the sulfoxidation of p-tolylmethylsulfide (TMS). Enzyme activity ranged from 4 to 30 nmol p-tolylmethylsulfoxide (TMSO)/30 min/mg cell protein for FMO 3 clones; for FMO 1 clones, the range was 1-6 nmol TMSO/30 min/mg. Cytotoxicity in these clones after exposure to thiocarbamate compounds was assessed by clonogenic assay. Thiourea (TU), phenylthiourea (PTU), and alpha-naphthylthiourea (ANTU) were toxic to FMO 3 cells but not to parental and FMO 1 clones; 50% toxicity was attained at 1x10(-4) M TU, 5x10(-6) M PTU, and 1x10(-6) M ANTU. Toxicity was observed after a minimum exposure time of 6 hr. Parental cells were resistant to toxicity for exposure times spanning the entire clonogenic assay period (10 days). Ethylene thiourea (ETU) was not toxic to FMO 3 cells, but preincubation with 1x10(-3) M ETU blocked TU toxicity. Reducing GSH levels by preincubation with 1x10(-5) M buthionine sulfoxime (BSO) increased TU sensitivity in FMO 3 cells from 1x10(-4) to 1x10(-6) M to achieve 50% toxicity. BSO also increased the sensitivity of "low expressor" FMO 3 clones to TU, but did not alter the refractoriness of either parental or FMO 1 expressing cells to TU. N-Acetylcysteine afforded modest protection to TU toxicity by shifting 50% cytotoxicity for TU from 5x10(-5) to 1x10(-3) M. TU mutagenicity was assayed by the development of ouabain resistance in parental and FMO 3 C3H/10T1/2 cells. Exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, direct acting mutagen) and TU was executed with and without prior sensitization with BSO. The mutation frequency for MNNG was 76/1x10(6) surviving cells, whereas no mutants were observed for TU-exposed cultures. The results of this study show that, in isolation, the major human hepatic form of FMO is capable of promoting thiocarbamate toxicity. Consistent with the known reactivity of thiocarbamate intermediates with GSH, treatments that alter GSH levels also altered toxicity in either the protective or sensitizing direction. These cell lines expressing variable levels of FMO 3 and TU sensitivity should prove useful as in vitro systems for dissecting the thiocarbamate toxicity pathway.

Iron chelation and hydroxyl radical scavenging reduce the inflammatory response of endothelial cells after infection with Chlamydia pneumoniae or influenza A

BACKGROUND

Chronic low-grade inflammation is associated with increased risk of vascular diseases. The source of inflammation is unknown but may well be chronic and/or repetitive infections with microorganisms. Direct infection of endothelial cells (ECs) may also be a starting point for atherogenesis by initiating endothelial procoagulant activity, increased monocyte adherence and increased cytokine production. We hypothesized that iron-mediated intracellular hydroxyl radical formation after infection is a key event in triggering the production of interleukin-6 (IL-6) by ECs in vitro.

METHODS

Cultured ECs were incubated with Fe(II) and Fe(III) or infected with Chlamydia pneumoniae or influenza A/H1N1/Taiwan/1/81 for 48 and 24 h, respectively. To determine the role of iron and reactive oxygen species, cells were coincubated with the H2O2 scavenger N-acetyl-l-cysteine, with the iron chelator deferoxamine (DFO) or with the intracellular hydroxyl radical scavenger dimethylthiourea (DMTU). After the incubation periods, supernatants were harvested for IL-6 determination.

RESULTS

Incubating ECs with Fe(II) and Fe(III) resulted in increased IL-6 production. Similarly, infection with C. pneumoniae and influenza A also induced an IL-6 response. Coincubating ECs with DFO or DMTU blocked this response. Nuclear factor-kappaB activity was increased after infection and blocked by coincubation with DFO or DMTU.

CONCLUSION

Cultured ECs respond to infection and iron incubation with increased production of IL-6. Iron, the generation of intracellular hydroxyl radical and NF-kappaB activity are essential in cellular activation, suggesting that reactive oxygen species generated in the Haber-Weiss reaction are essential in invoking an immunological response to infection by ECs.

Acute effects of pentobarbital, thiopental and urethane on lung oedema induced by alpha-naphthythiourea (ANTU)

This study was designed to investigate the possible participation of urethane, pentobarbital sodium and thiopental sodium anaesthesia in the lung oedema induced by alpha-naphthylthiourea (ANTU), which is a well known noxious chemical agent in the lung. ANTU when injected intraperitoneally (i.p.) into rats (10 mg x kg (-1) i.p.) produced lung oedema as indicated by an increase in lung weight/body weight (LW/BW) ratio and pleural effusion (PE) reaching a maximum within 4 h. Administration of urethane prior to ANTU, at doses of 100 and 200mg(100g)(-1), elicited a significant and dose-dependent inhibition in LW/BW ratio and PE. Thiopental sodium at doses of 25, 50 mg x kg (-1), also produced a significant and dose-dependent inhibition of both parameters. Prior i.p. injection of pentobarbital sodium at a dose of 40 mg x kg (-1) elicited a significant inhibition in both parameters. These results suggest that i.p. urethane, thiopental sodium and pentobarbital sodium pretreatment have a prophylactic effect on ANTU-induced lung injury in rats. The possible role of the anaesthetics in lung oedema induced by ANTU and the possible underlying mechanisms are discussed.

In vivo toxicity, pharmacokinetic features and tissue distribution of N-[2-(2,5-dimethoxyphenylethyl)]-N'-[2-(5-bromopyridyl)]-thiourea (HI-236), a potent non-nucleoside inhibitor of HIV-1 reverse transcriptase

N-[2-(2,5-Dimethoxyphenylethyl)]-N'-[2-(5-bromopyridyl)]-thiourea (HI-236, CAS 233271-65-3) possesses potent anti-viral activity against zidovudine-sensitive as well as multidrug-resistant HIV-1 (human immunodeficiency virus) strains. The purpose of the present study was to examine in vivo toxicity, pharmacokinetic features and tissue distribution of HI-236 in mice. HI-236 had an elimination half-life of 85.8 min after i.v. administration and 86.6 min after i.p. administration. The systemic clearance of HI-236 was 4337 ml/h/kg after i.v. administration and 10,130 ml/h/kg after i.p. administration. Following i.v. injection, HI-236 rapidly distributed to and accumulated in multiple tissues with particularly high accumulation in lung, adipose tissue, skin, urinary bladder, adrenal gland and uterus + ovary. The concentration of HI-236 in brain tissue was comparable to that in the plasma, indicating that HI-236 easily crosses the blood-brain barrier. Following i.p. injection, HI-236 was rapidly absorbed with a tmax values of 5.6 min and showed linear pharmacokinetics within the dose range of 10-80 mg/kg. Following oral administration, HI-236 was absorbed with a tmax of 5.8 min. The intraperitoneal bioavailability was estimated at 42.9%, while the oral bioavailability was only 2.2%. The pharmacokinetic study described herein provides the basis for advanced pharmacodynamic study of HI-236.

Evaluation of nitrification-inhibition measurements

A screening method for nitrification-inhibition determination has been evaluated at two laboratories, one in Sweden and one in Spain. Allyl-thiourea (ATU), methanol, chromium and zinc were used as reference toxicants in combination with different kinds of full-scale sludge and sludge produced in the laboratory. Different results were obtained with different combinations of activated sludge and toxicants. It was found that activated sludge often exposed to small amounts of a variety of toxic substances may build up a general resistance to toxic substances. Specific adaptation to certain substances was also observed. Domestic activated sludge responded in the same way to ATU regardless of whether it originated from Sweden or Spain. Synthetic sludge and domestic sludge exhibited the same inhibition of nitrification when tested with ATU as a toxicant. Synthetic activated sludge from two laboratory-scale plants run in parallel did not exhibit exactly the same sensitivity to certain toxicants. The variation in repeated tests with the synthetic sludges was about the same as for repeated tests with full-scale sludge and for other biological toxicity tests. Limits of detection were calculated to be about 5% for a single sample with three blanks as references at both the laboratories.

Large amount of vitamin A has no major effects on thyroidal hormone synthesis in two-stage rat thyroid carcinogenesis model using N-bis(2-hydroxypropyl)nitrosamine and thiourea

In our previous investigation, which focused on two-stage carcinogenicity in the thyroid, rats were administered N-bis(2-hydroxypropyl)nitrosamine (DHPN), followed by thiourea (TU) over an experimental period of 19 weeks. Simultaneous treatment with a high level of vitamin A (VA) enhanced the induction of proliferative lesions that originated from the thyroidal follicular epithelium. To examine whether hormone synthesis in the thyroid could be inhibited by simultaneous treatment with a large amount of VA and TU, all of the rats were initially given a single subcutaneous injection of 2,800 mg DHPN/kg followed by a supply of 0% TU + 0% VA (DHPN only, control group), 0.2% TU in their drinking water (DHPN/TU group), 0.1% VA in their diet (DHPN/VA group), or 0.2% TU + 0.1% VA (DHPN/TU + VA group) during an experimental period of 4 weeks. Results obtained indicate that the iodine uptake and organification, namely iodination of tyrosine residue in thyroglobulin, of the thyroid, were significantly decreased in the DHPN/TU group compared to the DHPN control group. The variation in these values was attributable to the inhibitory effect of TU upon thyroid hormone synthesis. Results obtained from the DHPN/TU + VA and DHPN/TU groups were comparable. Therefore, the possibility that modification of hormone synthesis contributes to the enhancing effect of simultaneous treatment with a large amount of VA on thyroidal tumor induction by TU is considered to be very minimal.

Evidence for the involvement of N-methylthiourea, a ring cleavage metabolite, in the hepatotoxicity of methimazole in glutathione-depleted mice: structure-toxicity and metabolic studies

In mice depleted of GSH by treatment with buthionine sulfoximine (BSO), methimazole (2-mercapto-1-methylimidazole, MMI) causes liver injury characterized by centrilobular necrosis of hepatocytes and an increase in serum alanine transaminase (SALT) activity. MMI requires metabolic activation by both P450 monooxygenase and flavin-containing monooxygenase (FMO) before it produces the hepatotoxicity. MMI and its analogues were examined for the ability to increase SALT activity in GSH-depleted mice. Saturation of the C-4,5 double bond in MMI resulted in a complete loss of hepatotoxicity. Similarly, ring fusion of a benzene nucleus to the C-4,5 double bond, forming 2-mercapto-1-methylbenzimidazole, abolished the toxic potency. As for MMI, 2-mercapto-1,4,5-trimethylimidazole, and 2-mercapto-1-methyl-4, 5-di-n-propylimidazole, the toxic potency decreased with the increasing bulk of the 4- and 5-alkyl substituents. Furthermore, methylation of the thiol group of MMI totally reduced its toxicity. These structural requirements and the known toxicity of thiono-sulfur compounds led us to the hypothesis that MMI would undergo epoxidation of the C-4,5 double bond by P450 enzymes and, after being hydrolyzed, the resulting epoxide would be then decomposed to form N-methylthiourea, a proximate toxicant. Before N-methylthiourea would produce toxicity, it would be further biotransformed to its S-oxidized metabolites mainly by FMO. Evidence for this hypothesis was provided by the facts that N-methylthiourea and glyoxal as the accompanying fragment were identified as urinary metabolites in mice treated with MMI and that N-methylthiourea caused a marked increase in SALT activity when administered to mice in combination with BSO.

Stimulated pulmonary cell hyperplasia underlies resistance to alpha-naphthylthiourea

The rodenticide alpha-naphthylthiourea (ANTU) causes pulmonary edema and pleural effusion that leads to death via pulmonary insufficiency. Rats become resistant to the lethal effect of ANTU if they are first exposed to a small, nonlethal dose of ANTU. Young rats are also resistant to ANTU. The mechanism by which rats develop resistance by a prior, small dose exposure has yet to be determined. Growth factor induced-pulmonary hyperplasia has been demonstrated to attenuate ANTU-induced lung leak. We hypothesized that a small dose of ANTU protects against a large dose through pulmonary cell hyperplasia induced by the protective dose. Furthermore, we hypothesized that this hyperplasia is associated with altered transcription of growth factors. Male Sprague-Dawley rats (175-225 g) were treated with a low dose of ANTU (5 mg ANTU/kg; ANTU(L)) 24 h before challenge with a 100% lethal dose of ANTU (70 mg ANTU/kg; ANTU(H)) resulting in 100% protection against the lethal effect of ANTU(H). ANTU(L) protection against ANTU(H) lasted for 5 days, slowly phased out, all being lost by day 20. Injury was assessed by estimating pulmonary vascular permeability and through histopathological examination. ANTU(H) alone resulted in an increase in pulmonary edema leading to animal death. However, injury was prevented if the rats were first treated with ANTU(L). There was a stimulation of pulmonary cell hyperplasia in the lungs of ANTU(L) treated rats as measured by [3H]-thymidine and bromodeoxyuridine incorporation. Treatment with the antimitotic agent colchicine abolished ANTU(L)-induced resistance to ANTU(H). ANTU resistant rats were also resistant to the lethal effect of paraquat. Paraquat is not taken up by pneumocytes if they are undergoing hyperplasia. ANTU(L) administration resulted in an up regulation of gene transcription for keratinocyte growth factor, transforming growth factor-beta, keratinocyte growth factor receptor and epidermal growth factor receptor as determined through reverse transcription-polymerase chain reaction. A significant increase in transforming growth factor-alpha was not observed. These findings collectively suggest that ANTU(L)-induced pulmonary cell hyperplasia underlies resistance to ANTU(H). Furthermore, the stimulation of hyperplasia may be due to altered growth factor and growth factor receptor expressions.

Immunohistochemical studies of TSH-producing cells in the pituitary and expression of growth factors in thyroidal proliferative lesions in rats treated with thiourea and excess vitamin A

Changes of TSH-producing cells in the pituitary and thyroid expression of the growth factors, transforming growth factor alpha (TGF alpha) and epidermal growth factor receptor (EGFR), as well as cyclin D1, were investigated immunohistochemically in order to clarify their contribution to the enhancing effects of excess vitamin A (VA) on thyroidal carcinogenesis induced by thiourea (TU). Male rats were allocated to 4 groups, control, TU, VA, and TU + VA, respectively, receiving no treatment, water containing 0.2% TU, diet containing 0.1% VA, and both for 10 or 19 weeks after a single s.c. injection of DHPN (2800 mg/kg) for initiation. Immunohistochemistry using antibodies against TSH demonstrated enlargement of TSH-producing cells in the TU + VA group as compared to the TU group, supporting our conclusion that enhanced TSH stimulation is mainly responsible for promoting the effects of excess VA. Since the expression of TGF alpha, EGFR, and cyclin D1 in thyroid proliferative lesions did not exhibit any differences between the TU and TU + VA groups in the present study, these factors are unlikely to participate in VA enhancement of carcinogenesis.

Free radicals generated in yeast by the Salmonella test-negative carcinogens benzene, urethane, thiourea and auramine O

A large fraction of carcinogens score negative in short-term genotoxicity assays such as the Salmonella reverse mutation (Ames) assay. More information is needed about the mechanism of action of such Salmonella-negative carcinogens. Many Salmonella-negative carcinogens induce deletions due to intrachromosomal recombination in Saccharomyces cerevisiae with an apparent threshold. We have previously shown that the Salmonella-negative carcinogens cadmium, aniline, chloroform and carbon tetrachloride generate free radical species in S. cerevisiae. We have further investigated the possible generation of intracellular free radical species by the diverse Salmonella-negative carcinogens benzene, urethane, thiourea and auramine O. The toxicity and recombinagenicity of thiourea and auramine O was reduced in the presence of the free radical scavenger N-acetyl cysteine. N-acetyl cysteine did not protect against toxicity or recombination induced by the Salmonella-positive carcinogens ethyl methane sulfonate, methyl methane sulfonate or nitroquinoline-N-oxide. A strain deficient in the enzyme superoxide dismutase, which catalyses the dismutation of superoxide anion radical, was hypersensitive to killing by benzene, urethane and thiourea. The sod- strain was only slightly more sensitive to the Salmonella-positive carcinogens. Intracellular oxidation of the free radical-sensitive reporter compound dichlorofluorescin diacetate was increased in yeast cultures exposed to benzene, urethane and auramine O; again, the Salmonella mutagens had no effect on oxidation of the dye. These data show that free radical species are produced in Saccharomyces cerevisiae following exposure to benzene, urethane, thiourea and auramine O, and suggest a possible role for oxidative stress is recombination induced by these carcinogens.

The guinea-pig skin sensitization test revisited: an evaluation formula to predict possible sensitization levels for eight chemicals used in household products

In predicting human skin sensitization due to possible risky chemicals, it is not sufficient to evaluate solely the minimum induction dose (MID) or the standard challenge dose (SCD) in the Guinea Pig Maximization Test (GPMT). Nakamura et al. (1994) (Nakamura, A., Momma, J., Sekiguchi, H., Noda, T., Yamano, T., Kaniwa, M., Kojima, S., Tsuda, M., Kurokawa, Y., 1994. A new protocol and criteria for quantitative determination of sensitization potencies of chemicals by guinea pig maximization test. Contact Dermatitis 31, 72-85) previously measured the residual dose of chemicals in the products implicated in human allergic accidents, and stated that '... the level of chemical in the products (direct exposure-dose = DED) was similar to or higher than value of sensitization potency.' However, several of the chemicals listed in their article, show an even lower value of sensitization potency than the DED, although a potential correlation between results of the GPMT and the DED was seemed to be evident; a key question about the essential rule of those parameters therefore remains open. Using the data of Nakamura et al. (1994), we analyzed the functional rules of the three independent parameters, the MID, the SCD, and the DED on which the GPMT is based. Calculations of the degree of allergic reactions elicited in humans provided a range of discrimination constants (D) using the formula; D = DED/(MID*SCD). Possible human allergic accidents may be predicted when the dose of a candidate chemical in a chemical product (equal to DED) exceeds the value; D*(MID*SCD), following the correct evaluation of the MID as well as the SCD.

Cytotoxicity of a series of mono- and di-substituted thiourea in freshly isolated rat hepatocytes: a preliminary structure-toxicity relationship study

The cytotoxicity of a series of 12 mono- and 4 di-substituted thiourea containing compounds in freshly isolated rat hepatocytes was investigated. It was found that thiourea toxicity, as evidenced by an increase in LDH-leakage from the cells, was accompanied by a depletion of intracellular glutathione (GSH). No increase in lipid peroxidation was observed with any of the thiourea. Burimamide and thioperamide, thiourea-containing histamine receptor ligands, were also found to deplete intracellular GSH. A clear structure-toxicity relationship was uncovered among a homologous series of N-phenylalkylthiourea. N-benzylthiourea (BTU) and N-phenylethylthiourea (PETU) were found to be non-toxic at a concentration of 1 mM, while N-phenylpropylthiourea (PPTU) and N-phenylbutylthiourea (PBTU) were found to cause significant LDH-leakage from the cells, accompanied by a depletion of intracellular GSH. This structure-toxicity relationship was further investigated using hepatocytes of differentially induced rats, however, no significantly different results were obtained when using hepatocytes of rats induced with phenobarbital (PB) or beta-naphthoflavone (BNF). Oxidation of the thiourea moiety is thought to be the first step in the bioactivation of thiourea containing compounds. The oxidation of thiocholine sulfenic acids, produced by FMO-mediated oxidation of the thiourea moiety, was used to determine whether the compounds examined are substrates for the FMO enzymes in rat liver. No clear relationship was found between cytotoxicity of the mono-substituted thiourea and lipophilicity of the N-substituent, nor with the FMO-mediated oxidation of the thionosulfur atom of the mono-substituted thiourea. It is concluded from this study, that thiourea toxicity in rat hepatocytes is structure-dependent and manifests itself as LDH-leakage and as a depletion of intracellular non-protein sulfhydryls, notably GSH, most likely followed by alkylation of vital macromolecular structures.

Genotoxic activation of hydrazine, two dialkylhydrazines, thiourea and ethylene thiourea in the somatic w/w + assay of Drosophila melanogaster

Genotoxic activation of hydrazine (HZ), two symmetrical dialkylhydrazines, namely, 1,2dimethylhydrazine and 1,2-diethylhydrazine (SDMH and SDEH), thiourea (TU) and ethylene thiourea (ETU) has been evaluated by means of the w/w + somatic assay of Drosophila. Both low bioactivation insecticide-susceptible (IS) and high biotransformation insecticide-resistant (IR) strains were used. The combined application of insecticide-susceptible and insecticide-resistant strains should, in principle, detect somatic cell recombinagens in the Drosophila melanogaster in vivo w/w + assay. The IS strain was more susceptible to toxicity induced by the test chemicals than the IR stocks. Its performance in the biotransformation of the chemicals tested was rather poor. TU was inactive in all strains. With the active compounds, spot frequencies increased approximately linearly with dose for each spot type. SDEH gave a strong positive result in all three female genotypes exposed. HZ, ETU and SDMH were overall weakly positive in the IR strain Haag-79 (HG-R). Interestingly, ETU was clearly positive in the IR Hikone-R (HK-R) strain. A comparison of the recombinagenic potencies between the active and the weakly positive compounds, and among strains, showed pronounced genotype-dependent differences between the low and the high bioactivation strains. The ability of Drosophila to express several procarcinogens in relation to insecticide-resistance after activation catalyzed by CYP450 enzymes is discussed.

Effects of the paralytic agent 2,4-dithiobiuret on viability and morphology of rat pheochromocytoma (PC12) cells

In previous studies, 2,4-dithiobiuret (DTB) caused a delayed onset neuromuscular weakness in rats which was associated with decreased quantal content, alterations in postsynaptic ion channel properties, and abnormalities in nerve terminal ultrastructure. The latter include features typical of degenerating or diseased motor endplates as well as a marked proliferation of smooth endoplasmic reticulum (SER), swelling of mitochondria and evidence for a decreased in intraterminal calcium concentrations at early stages of intoxication (Jones, 1989, Acta Neuropathol. 78:72). These in vivo studies do not allow us to distinguish between the initial effects of DTB on the nerve terminal and those evolving as a result of disuse or secondary to its action on the muscle fiber or Schwann cells. To begin to distinguish between primary and secondary effects of DTB, we examined DTB-treated rat PC12 cells for comparable changes. The direct effects of DTB on PC12 cells included signs of general toxicity. Cell death in sparsely- plated cultures increased from 8-9% in controls to 13.7% at 10 microM for 24 hr exposure, and continued to increase in a concentration-dependent fashion to 25% mortality at 25 microM. However, between 25 and 100 microM there was little additional increase in mortality. 10 to 40 microM DTB slightly decreased the ability of both differentiated and undifferentiated cells to adhere to a substrate. This effect was independent of cell mortality. In moderately-differ-entiated cells having processes up to 10 cell diameters and several varicosities, concentrations of DTB as high as those invoking increased cell mortality and comparable to those affecting the rat neuromuscular junction did not cause abnormalities in the structure of the SER. No masses of tubulovesicular profiles were seen with transmission electron microscopy, and large changes in the quantity or distribution were not detected at the light microscope with the fluorescent stains DiOC6 or rhodamine B. Other signs of neuronal degeneration (blebbing of the plasmalemma, large intracellular droplets, mitochondrial abnormalities) preceded or accompanied any evidence for abnormalities in the SER. Thus the effect of DTB on the SER at the rat motor nerve terminal may occur secondary to a more general toxic action on other cell types, or may be dependent on a level of neuronal activity not achieved in sparsely- plated cultures, or may require a greater degree of differentiation of the neuronal cells than provided by the PC12 cell model used in this study.

Effect of ethylene thiourea on cultured rat embryos in the presence of hepatic microsomal fraction

To investigate whether teratogenicity of ethylene thiourea (ETU) is due to ETU per se or to its metabolites, rat embryos cultured in vitro were exposed to 10 and 30 micrograms/ml of ETU in the presence or absence of rat liver microsomal fraction (S9mix). In the absence of S9mix, the incidence of morphological abnormalities increased dose-dependently. In the presence of S9mix, abnormal morphogenesis was almost absent in all embryos. These findings suggest that teratogenicity of ETU is due to ETU per se.

Increase of lung sodium-potassium-ATPase activity during recovery from high-permeability pulmonary edema

Previous studies have suggested that recovery from pulmonary edema may be dependent on active sodium ion transport. Most of the data supporting this concept came from work done in isolated type II cells, isolated lung preparations, or in models of alveolar flooding. There is a limited amount of information regarding the role of active sodium ion transport in vivo. Furthermore, most of this information was obtained in one model of pulmonary edema, the hyperoxic lung injury model. The purpose of these experiments was then to measure the activity of the sodium-potassium-adenosinetriphosphatase (Na(+)-K(+)-ATPase), the active component of the sodium transport process and an indirect marker of active sodium transport, during recovery from thiourea-induced pulmonary edema in rats. Na(+)-K(+)-ATPase activity was significantly increased during recovery from lung edema. This increase could not be accounted for by the Na(+)-K(+)-ATPase activity present in inflammatory cells recruited in the lung by the injury process or by a direct impact of thiourea on the enzyme. Alveolar flooding, induced by instillation of a protein-containing solution into the airways of ventilated rats also increased the activity of Na(+)-K(+)-ATPase, suggesting that activation of the enzyme is probably secondary to either the presence of edema or the physiological consequences associated with edema. The quantity of lung Na(+)-K(+)-ATPase protein was also elevated during edema resolution, indicating that augmented synthesis of this enzyme underlies the increased enzyme activity observed. The quantity of Na(+)-K(+)-ATPase protein in alveolar type II cells was also significantly enhanced during recovery from edema, suggesting that these cells contribute to active sodium transport in vivo. The results of this study suggest that active sodium transport could participate in the resolution of pulmonary edema.

Promoting effect of large amounts of vitamin A on cell proliferation of thyroid proliferative lesions induced by simultaneous treatment with thiourea

In order to examine modifying effects of simultaneous treatment with large amounts of vitamin A (VA) and thiourea (TU) on the thyroid tumorigenesis in rats, male F344 rats were initiated with N-bis(2-hydroxypropyl)nitrosamine (2800 mg/kg body weight, single s.c. injection), and starting 1 week later received diet containing 0.1% VA (VA group), drinking water containing 0.2% TU (TU group), 0.2% TU + 0.1% VA (TU + VA group) or tap water/basal diet (control group) for 19 weeks. Serum T3 and T4 in the TU and TU + VA groups were significantly decreased as compared to the control group, while serum TSH levels were remarkably increased. The ratios of T3 and T4 decrease and TSH increase in the TU + VA group were remarkably more pronounced than in the TU group. Thyroid neoplastic lesions were only induced in the TU and TU + VA groups. The multiplicity of intracapsular follicular cell proliferative foci in the TU + VA group was significantly increased as compared to the TU group value. Cell proliferation of hypertrophic and subcapsular follicular cells, as well as in hyperplasias, and neoplasias with adenomatous growth pattern was significantly higher in the combined treatment case than after TU alone. In the liver, centrilobular hypertrophy of hepatocytes was seen in the TU and TU + VA groups, this being especially marked in the latter group. In the combined group case the affected cells were strongly positive for GST-P antibody binding. The results of the present study suggest that cell proliferation of thyroid follicular cell proliferative lesions in rats is enhanced by strong TSH stimulation with simultaneous treatment of TU and large amounts of VA.