Inhibitory effects of aminoguanidine on thyroid follicular carcinoma development in inflamed capsular regions of rats treated with sulfadimethoxine after N-bis(2-hydroxypropyl)nitrosamine-initiation

We have reported that thyroid capsular thickening with inflammation induced by an antithyroidal agent, sulfadimethoxine (SDM), might play a role in the development of invasive follicular carcinomas in rats initiated with N -bis(2-hydroxypropyl)nitrosamine (DHPN). Inducible nitric oxide synthase (iNOS) expressed in the inflamed capsular regions further appeared to be implicated in the tumor progression. In the present study, the effects of an iNOS inhibitor, aminoguanidine (AG), on thyroid carcinogenesis were examined. F344 male rats were treated with SDM in drinking water (0.1%) with or without concomitant dietary administration of AG (0.2%) for 4 and 10 weeks after subcutaneous injection of DHPN at 2800 mg/kg bodyweight. At week 4, thyroid capsular thickening with inflammation was observed and iNOS-positive foci were found in the inflamed regions. In addition, single-strand DNA-positive inflammatory cells were scattered among neighboring follicular cells, indicating some cellular damage, at least partly in association with iNOS induction. Concurrent dietary administration of AG with SDM treatment slightly decreased the number of single-strand DNA-positive cells but did not alter the incidence and multiplicity of iNOS-positive foci in the inflamed capsular regions at week 4. At week 10, however, invasive follicular carcinomas predominantly arose in the thickened capsule in the DHPN–SDM-treated rats, and AG administration decreased ( P  < 0.05) their multiplicity. The carcinoma cells were partly positive for iNOS. These results thus suggested that iNOS induction in both inflammatory and tumor cells might play pivotal roles in tumor progression in this DHPN–SDM rat model. ( Cancer Sci  2009; 100: 1794–1800)     

Development of invasive follicular cell carcinomas in a rat thyroid carcinogenesis model: biological impact of capsular inflammation and reduced cyclooxygenase-2 expression

We have previously reported that thyroid capsular inflammation induced by sulfadimethoxine (SDM), a goitrogen, might play a role in development of invasive follicular cell adenocarcinomas in rats initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). The present study was designed to examine the role of cyclooxygenase (COX)-2, widely known to be up-regulated in inflammatory states, during chemically induced rat thyroid carcinogenesis. Male F344 rats received a subcutaneous DHPN (2800 mg/kg) injection, and 1 week later were allowed free access to drinking water containing antithyroidal propylthiouracil (PTU, 0.003%) or SDM (0.1%) for 4 or 10 weeks. Control groups receiving goitrogen alone and no treatment were also included. At week 4, diffuse follicular cell hyperplasia was induced in all PTU- and SDM-treated groups, along with fibrous capsular thickening and capsular thickening with inflammation, respectively. Additionally, multiple focal follicular cell hyperplasias and adenomas were observed in the DHPN + PTU and DHPN + SDM cases. At week 10, adenocarcinomas invasive to the capsule and restricted to the capsular adjacent region, were frequent in the DHPN + SDM group, but not observed in the animals given DHPN + PTU. Western blots and immunohistochemistry revealed constitutive COX-2 expression in non-neoplastic follicular cells of the control and all of the PTU- and SDM-treated rats. However, COX-2 reactivity was significantly reduced or negative in the preneoplastic/neoplastic lesions in the DHPN-treated groups. In fibrous or inflamed thickened capsules, only a few component cells with inflammatory elements were positive for COX-2, and there was no significant difference in this regard between the PTU and SDM treatments. The present results suggest that capsular inflammation could play a role in development of invasive carcinomas, but COX-2 expression does not make a major contribution.     

Possible single dosage effects of the nude gene: suppression of spontaneous development of thymoma and nephropathy in BUF/Mna-rnu/+ rats

Single dosage effects of the rat nude gene (rnu) on spontaneous development of epithelial thymoma, muscle atrophy and nephrotic syndrome were studied by comparing littermates of rnu /+ and +/+ rats on a high thymoma strain, BUF/Mna, background. Heterozygous rnu/+ rats had a significantly smaller thymus than the +/+ littermates at 6 weeks of age. The incidence of thymoma at 12 months of age was extremely low in the female rnu/+ rats (3%) as compared with that of the +/+ rats (94%). Development of the nephrotic syndrome but not of the muscle atrophy was also suppressed in the heterozygotes. The results suggest that a recessive mutant gene, rnu, in a single dosage, interfered with critical steps of the disease processes of the thymoma and nephrotic syndrome in BUF/Mna-background rats.     

Effect of propylthiouracil on the thyroid tumorigenesis induced by N-bis(2-hydroxypropyl)nitrosamine in rats

The effect of 0.15% propylthiouracil (PTU) on thyroid tumorigenesiswas studied in male Wistar rats given a single i.p. injectionof 280 mg of N-bis(-2-hydroxypropyl)nitros-amine (DHNP) per100 g body weight. The mean weights of the thyroid of rats treatedwith DHPN followed by PTU and with PTU alone were significantlyhigher than those of rats treated with DHPN only and controlrats. The incidences of follicular adenoma at the end of week20 of the experiment were 100% (21/21) hi rats treated withDHPN followed by PTU, and 19% (4/21) hi rats given DHPN alone.Papillary adenoma was observed in one rat treated with DHPNfollowed by PTU. The incidence of follicular carcinomas withinvasive growth into the capsule, adipose tissues or blood vesselswas 52% (11/21) in rats given DHPN and then PTU. No papillarycarcinomas or solid tumors were found in any rats. Rats givenPTU alone and untreated rats had no thyroid tumors. The serumconcentration of T₄ in rats treated with PTU alone was significantlylower than that hi the control group. The serum concentrationof T₄ in rats treated with DHPN followed by PTU was slightly,but not significantly, lower than that in control rats. Theserum concentrations of T₃ in rats treated with DHPN foDowedby PTU, DHPN alone and PTU alone were also slightly, but notsignificantly, lower than that in controls.     

Nitric oxide of human colorectal adenocarcinoma cell lines promotes tumour cell invasion

The present study investigates the role of nitric oxide and the involvement of nitric oxide synthase II isoform on the invasion of human colorectal adenocarcinoma cell lines HRT-18 and HT-29. HRT-18 cells, which constitutively express nitric oxide synthase II mRNA were three-fold more invasive in a Matrigel invasion assay than nitric oxide synthase II mRNA negative HT-29 cells. Treatment of HT-29 cells with the nitric oxide donor Deta NONOate (50 nM) as well as induction of nitric oxide synthase II mRNA and production of endogenous nitric oxide by inflammatory cytokines (IFN-gamma and IL-1alpha) increased the invasiveness of HT-29 cells by approximately 40% and 75%, respectively. In HT-29 cells nitric oxide synthase II mRNA was also induced in co-culture with human monocytes. The invasiveness of HRT-18 cells and stimulated HT-29 cells was partly inhibited by the nitric oxide synthase II inhibitor 1400 W. These results show that nitric oxide increases the invasion of human colorectal adenocarcinoma cell lines HRT-18 and HT-29, and the involvement of nitric oxide synthase II isoform in tumour cell invasion. Therefore, the production of nitric oxide and secretion of pro-inflammatory cytokines by tumour-associated macrophages, which in turn induce nitric oxide synthase II isoform in tumour cells, promotes tumour cell invasiveness.     

Greater inhibitory effects for testosterone than castration in rat thyroid tumorigenesis initiated by N-bis(2-hydroxypropyl)nitrosamine

The effects of testosterone and castration on thyroid tumorigenesis subsequent to initiation by N-bis(2-hydroxypropyl)nitrosamine (DHPN) were investigated in male Wistar rats. Following 2 weekly i.p. injections of DHPN at the dose of 210 mg/100 g body weight, testosterone was administered in the diet at concentrations of 0.15% or 0.03% for 28 weeks. Castration was performed on a separate group of animals 1 week after the final injection of DHPN. The incidence of thyroid adenomas and carcinomas were 69% (9/13) and 15% (2/13), respectively, in rats treated with DHPN alone, 0% (0/15) and 6% (1/15) in rats treated with DHPN and 0.15% testosterone, 13% (2/15) and 13% (2/15) in rats treated with DHPN and 0.03% testosterone and 33% (5/15) and 33% (5/15) in the castrated animals initiated by DHPN. The reduction in adenoma development associated with testosterone treatment was significant at both concentrations. In contrast, only a tendency for decrease of thyroid tumor incidence was observed in rats castrated.     

The promoting effects of food dyes, erythrosine (Red 3) and rose bengal B (Red 105), on thyroid tumors in partially thyroidectomized N-bis(2-hydroxypropyl)-nitrosamine-treated rats

The effects of erythrosine (Red 3), rose bengal B (Red 105) and thyroidectomy on the development of thyroid tumor were examined in male Wistar rats treated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). Red 3 and Red 105 were used at 4% in the basal diet and were administered for 19 weeks from week 2 to 20. Thyroidectomy was performed by resection of the left lobe at week 4. Single injection of DHPN was performed intraperitoneally at 280 mg per 100 g body weight at the beginning of the experiment. Red 3 and Red 105 significantly promoted the development of thyroid tumors in thyroidectomized rats given DHPN, but had no significant effect in non-thyroidectomized rats. The incidence of thyroid tumors was 91% in rats with partial thyroidectomy, Red 3 and DHPN, 100% in rats with partial thyroidectomy, Red 105 and DHPN, and 64% in rats with partial thyroidectomy and DHPN. Serum TSH was 5.5 +/- 3.1 ng/ml in rats with partial thyroidectomy, Red 3 and DHPN, 2.1 +/- 2.2 ng/ml in rats with partial thyroidectomy, Red 105 and DHPN, and 1.5 +/- 0.5 ng/ml in rats with partial thyroidectomy and DHPN.     

Potassium perchlorate, potassium iodide, and propylthiouracil: promoting effect on the development of thyroid tumors in rats treated with N-bis(2-hydroxypropyl)-nitrosamine

The effect of 1000 ppm potassium perchlorate (KClO4), 1000 ppm potassium iodide (KI) or 1000 ppm propylthiouracil (PTU) in the diet on the development of thyroid tumors was studied histologically and biochemically in Wistar rats given a single ip injection of 280 mg of N-bis(2-hydroxypropyl)nitrosamine (DHPN) per 100 g body weight. Basal diet containing 100 ppm KClO4, 1000 ppm KI or 1000 ppm PTU was given for 19 weeks from week 2 to week 20. The incidence of thyroid adenomas at the end of week 20 of the experiment was 100% (20/20) in rats treated with DHPN followed by KClO4, 85% (17/20) in rats given DHPN followed by KI, 95% (19/20) in rats given DHPN followed by PTU, and 5% (1/20) in rats given DHPN alone. The incidence of thyroid cancers was 100% (20/20) in rats treated with DHPN followed by KClO4, 65% (13/20) in rats treated with DHPN followed by KI and 0% (0/20) in rats treated with DHPN followed by or not followed by PTU. Rats given KClO4, KI or PTU alone and untreated rats had no thyroid tumors. The mean values of TSH in serum were 2.94 +/- 0.79 ng/ml in rats treated with DHPN followed by KClO4, 9.40 +/- 16.0 ng/ml in rats treated with DHPN followed by KI and 60.94 +/- 20.60 ng/ml in rats treated with DHPN followed by PTU. It was confirmed that (1) KClO4, PTU and KI promote the development of thyroid tumor in rats treated with DHPN, (2) the promoting effect of KClO4 or KI is stronger than that of PTU and (3) the value of TSH in serum is not parallel to the promoting effect on the development of thyroid tumor.     

Antibody response of nude (RNU/RNU) and hairy (RNU/+) rats to circulating cell surface components from human pancreatic cancer xenografts.

Homozygous nude rats (rnu/rnu) injected s.c. with 3 X 10(7) human pancreatic cancer cells from the GER cell line developed circulating antibody to GER cell surface, detected in a 125I binding assay against viable GER cells in vitro. Antibody titre rose with progressive xenograft growth. These antibodies showed no selectivity for GER cells when compared with a panel of other human cell lines. Heterozygous nude rats (rnu/+) immunised with serum from their GER xenograft-bearing nude relatives (rnu/rnu) also developed anti-GER cell surface antibodies. These antibodies showed some selectivity for GER and WAD (a second human pancreatic cancer cell line) when compared with other human cancer cells and lymphocytes. These findings show that some human pancreatic cancer cell surface components may persist independently in the circulation of xenograft bearing rnu/rnu rats despite the presence of antibody excess to other surface determinants from the same cells. It is suggested that differences in the relative immune competence of rnu/rnu and rnu/+ rats may offer a biological opportunity for enhancing the recognition of weak antigenic determinants which may have some useful selectivity for different types of human tumour cells.     

Synergistic interaction between excess caffeine and deficient iodine on the promotion of thyroid carcinogenesis in rats pretreated with N-bis(2-hydroxypropyl)nitrosamine

The combined effects of caffeine (1,3,7-trimethylxanthine) with iodine deficiency (ID) were examined in a rat two-stage thyroid carcinogenesis model using N -bis(2-hydroxypropyl)nitrosamine (DHPN). Male F344 rats were divided into 6 groups each consisting of 10 animals, and received a single s.c. injection of 2800 mg/ kg DHPN. From 1 week after the DHPN initiation, the rats were respectively fed a basal diet in which the protein was exchanged for 20% gluten, containing 1500 ppm caffeine+ID, 300 ppm caffeine+ID, 60 ppm caffeine+ID, 1500 ppm caffeine or ID or a basal diet alone for 12 weeks. Relative thyroid weights were significantly (P<0.05) increased due to the development of prolifera-tive lesions induced by the ID diet as compared to the DHPN-alone group value, which was enhanced by caffeine, albeit without statistical significance. Relative pituitary weights were significantly (P<0.05) increased with 300 or 1500 ppm caffeine+ID as compared to the DHPN-alone group value. Serum thyroid stimulating hormone (TSH) levels were slightly increased by ID, an effect which was further enhanced by 300 or 1500 ppm caffeine. Serum thyroxine (T₄) levels were slightly increased by caffeine or ID alone, but decreased by caffeine with ID. Histopathologically, thyroid follicular carcinomas were found only in the 1500 ppm caffeine+ID group, although thyroid follicular adenomas were detected in all the ID-treated groups. The multiplicity of focal thyroid follicular hyperplasias was significantly (P<0.05) increased by 1500 ppm caffeine. These results indicate that caffeine may synergistically promote thyroid carcinogenesis with ID partially through a pituitary-dependent pathway in rats, implying the possible implication of routine caffeine intake in the promotion of thyroid carcinogenesis. (Cancer Sci 2003; 94: 334–337)     

Effects of chrysotile asbestos on lung and pleural carcinogenesis of N-bis(2-hydroxypropyl)nitrosamine in rats

The effects of chrysotile asbestos on lung and pleural carcinogenesis by N-bis(2-hydroxypropyl)nitrosamine (DHPN) in male Wistar rats were studied. Chrysotile, 30 mg per rat, was injected into the left pleural cavity and 3 g/kg body wt. DHPN was injected once into the abdominal cavity. Lung tumors (adenoma, adenocarcinoma, squamous cell carcinoma, and combined carcinoma) occurred at the highest incidence (100%). Adenocarcinoma was seen in 4 of 11 (36%) rats killed at 35 weeks and in 6 of 12 (50%) rats killed at 52 weeks, squamous cell carcinoma occurred in 1 of 11 (9%) rats killed at 35 weeks and 3 of 12 (25%) rats killed at 52 weeks, and mixed carcinoma was seen in 1 of 12 (8%) rats killed at 52 weeks, which received chrysotile and DHPN. Adenocarcinoma was seen in 9 of 11 (82%) rats which received DHPN only and killed at 52 weeks. Mesotheliomas were seen in 2 of 11 (18%) rats, killed at 35 weeks, and 3 of 12 (25%) rats, killed at 52 weeks, which received chrysotile and DHPN. Hyaline thickening of the pleura was seen in 100% of rats receiving chrysotile. Mesothelial cell hyperplasia and adenomatous and/or fibromatous growth of the mesothelium were seen in the pleura on both sides, ranging from 36% to 50% and 31% to 64% in rats receiving chrysotile and DHPN, respectively. Asbestos bodies were seen in the pleura on both sides and in the lung.     

Colorectal carcinoma development in inducible nitric oxide synthase-deficient mice with dextran sulfate sodium-induced ulcerative colitis

The overproduction of reactive oxygen and nitrogen species (RONS) may play an important role in ulcerative colitis (UC)-associated carcinogenesis. In order to study the role of nitric oxide (NO) in UC-associated colorectal carcinogenesis, the development of colorectal carcinoma was studied using the DSS-induced and iron-enhanced model of chronic UC in inducible nitric oxide synthase (iNOS)-deficient mice. Female wild-type C57BL/6 (iNOS+/+) and iNOS-/- mice were administered 1% DSS (w/v) through the drinking fluid for 15 DSS cycles and fed twofold iron-enriched diet. Colorectal inflammation and mucosal ulceration of moderate severity were observed in both iNOS+/+ and iNOS-/- mice. Similar tumor incidence and multiplicity in the colon were observed that 15 out of 23 (65.2%) iNOS+/+ mice developed colorectal tumors with a tumor multiplicity of 1.47+/-0.17 (mean+/-SE) after 15 DSS cycles, and 13 out of 19 (68.4%) iNOS-/- mice developed colorectal tumors with a tumor multiplicity of 2.08+/-0.21. Histopathologically, the tumors were confirmed to be well-differentiated adenocarcinomas. Nitrotyrosine, an indicator of peroxynitrite-caused protein modification, was detectable by immunohistochemistry in inflammatory cells and epithelial cells of the colon in iNOS+/+ and iNOS-/- mice, and no difference in staining intensity was observed between the two groups. Immunostaining for endothelial NOS (eNOS) was observed in lamina propria macrophages and colonic blood vessels, and eNOS protein levels were increased in the inflamed colon. These results show that there is no difference in UC-associated cancer development in iNOS+/+ and iNOS-/- mice, and suggest that in the absence of iNOS, other factors, such as eNOS, may play a role in nitrosative stress and UC-associated carcinogenesis in this model system.     

Comparison of enhancing effects of different goitrogen treatments in combination with beta-estradiol-3-benzoate for establishing a rat two-stage thyroid carcinogenesis model to detect modifying effects of estrogenic compounds

With the aim of establishing a sensitive model for the detection of weak effects of endocrine disrupting chemicals on thyroid carcinogenesis, thyrotrophic and tumor-promoting influences of beta-estradiol-3-benzoate (EB) in combination with representative antithyroidal agents (goitrogens), sulfadimethoxine (SDM), propylthiouracil (PTU), potassium perchlorate (PPC), iopanoic acid (IOP) or an iodine-deficient diet were evaluated in a short-term (7-day) experiment without N-bis(2-hydroxypropyl)nitrosamine (DHPN) initiation and a long-term (30-week) experiment with DHPN initiation in ovariectomized F344 rats. In the short-term experiment, the most remarkable thyrotrophic effects were found in the PTU-treated group, followed by the SDM and PPC cases. EB treatment alone caused slight increases in thyroidal weights but no apparent morphological changes. Concomitant treatment with EB and antithyroidal agents enhanced the changes in thyroid weights, histopathological findings and/or serum thyroid hormone levels in the SDM (30 and 100 p.p.m), PTU (5 and 30 p.p.m) and PPC (100 p.p.m), IOP (30 and 100 mg/kg) or iodine-deficient diet groups. In the long-term experiment after DHPN initiation, EB alone slightly increased small numbers of animals with follicular hyperplasias, adenomas and adenocarcinomas. Simultaneous treatment with antithyroidal chemicals was associated with an increase in the incidences of focal hyperplasias, adenomas and/or adenocarcinomas. The enhancement was most remarkable with PTU (5 p.p.m), followed by PTU (2 p.p.m), SDM (100 p.p.m) and PPC (100 p.p.m). The results showed that EB has only a marginal promoting effect on DHPN-induced rat thyroid carcinogenesis and that antithyroidal chemicals, particularly PTU, are effective as co-promoting agents.     

Inhibitory effects of antioxidants on N-bis(2-hydroxypropyl)nitrosamine-induced lung carcinogenesis in rats

Potential second-stage modifying effects of 8 antioxidants on lung tumorigenesis initiated by N-bis(2-hydroxypropyl)nitrosamine (DHPN) were examined in male F344 rats. After an initial 2-week treatment with DHPN (0.1% in drinking water), rats were administered one of the antioxidants supplemented in the diet for 30 weeks. Although the incidences of lung adenomas were not affected, those of carcinomas were lowered by 2% butylated hydroxyanisole (BHA, 2 rats/20 rats), 1% butylated hydroxytoluene (BHT, 1/20), 0.8% ethoxyquin (EQ, 3/20) and 1% a-tocopherol (a-TP, 2/20) treatments as compared to the control level (9/20), while 5% sodium L-ascorbate (SA), 0.8% catechol (CC), 0.8% resorcinol (RN), and 0.8% hydroquinone (HQ) did not exert any significant effect on incidence. Quantitative analysis of adenomas and carcinomas (numbers and areas of lesions per unit area of lung section) revealed obvious inhibitory effects of SA, CC, and RN as well as BHA, BHT, EQ, and a-TP. Among the antioxidants, BHT exerted the strongest inhibitory activity. In contrast, DHPN-induced thyroid tumorigenesis was significantly enhanced by BHT (14/20) and EQ (20/20) treatments (control = 5/20). Thus the antioxidants showed opposite effects on lung and thyroid carcinogenesis in the rat.     

Inhibitory Effects of Antioxidants on N-Bis(2-hydroxypropyl)nitrosamine-induced Lung Carcinogenesis in Rats

Potential second-stage modifying effects of 8 antioxidants on lung tumorigenesis initiated by N-bis(2-hydroxypropyl)nitrosamine (DHPN) were examined in male F344 rats. After an initial 2-week treatment with DHPN (0.1% in drinking water), rats were administered one of the antioxidants supplemented in the diet for 30 weeks. Although the incidences of lung adenomas were not affected, those of carcinomas were lowered by 2% butylated hydroxyanisole (BHA, 2 rats/20 rats), 1% butylated hydroxytoluene (BHT, 1/20), 0.8% ethoxyquin (EQ, 3/20) and 1%α-tocopherol (α-TP, 2/20) treatments as compared to the control level (9/20), while 5% sodium l -ascorbate (SA), 0.8% catechol (CC), 0.8% resorcinol (RN), and 0.8% hydroquinone (HQ) did not exert any significant effect on incidence. Quantitative analysis of adenomas and carcinomas (numbers and areas of lesions per unit area of lung section) revealed obvious inhibitory effects of SA, CC, and RN as well as BHA, BHT, EQ, and α-TP. Among the antioxidants, BHT exerted the strongest inhibitory activity. In contrast, DHPN-induced thyroid tumorigenesis was significantly enhanced by BHT (14/20) and EQ (20/20) treatments (control=5/20). Thus the antioxidants showed opposite effects on lung and thyroid carcinogenesis in the rat.     

Immunohistochemical expression of inducible nitric oxide synthase in DMBA-induced hamster buccal pouch carcinogenesis

Nitric oxide (NO) plays a key role in the processes of inflammation and carcinogenesis. Three isoforms of NO synthase have been identified: endothelial nitric oxide synthase (NOS), neuronal NOS, and inducible NOS (iNOS). The purpose of this study was to investigate the characteristics of iNOS in 7, 12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. Thirty outbred young (6-week-old) male Syrian golden hamsters were randomly divided into three groups: DMBA (0.5%) painted group (n=10); mineral oil-treated group (n=10); and non-treated group (n=10). The average number of iNOS positive foci per section in the DMBA-treated group was approximately 12.2+/-4.7. Both cytoplasmic and nuclear stainings were observed in the DMBA-treated pouch keratinocytes. No iNOS activity could be detected in the untreated or mineral oil-treated pouches. In conclusion, this study has demonstrated that iNOS is expressed in DMBA-induced hamster pouch carcinomas. This finding suggests that iNOS expression may be associated with the development of chemically induced oral carcinomas.     

Promoting effects of xylazine on development of thyroid tumors in rats initiated with N-bis(2-hydroxypropyl)nitrosamine and the mechanism of action

To cast light on whether xylazine hydrochloride (XZ), a veterinary medicine commonly used as a sedative agent for food-producing animals, has any promoting potential for thyroid carcinogenesis, the following studies were performed. In Experiment I, male F344 rats received a diet containing 1000 or 0 p.p.m. XZ for 52 weeks with or without initiation with 2400 mg/kg N:-bis(2-hydroxypropyl)nitrosamine (DHPN). Focal follicular cell hyperplasias, adenomas and/or carcinomas were induced in the DHPN alone, XZ alone and DHPN+XZ groups, and the incidences and multiplicities of these lesions in the DHPN+XZ group were significantly increased as compared with the DHPN alone case. In Experiment II, male F344 rats received a diet containing 1000 or 0 p.p.m. XZ and were examined for serum levels of triiodothyronine (T(3)), thyroxine (T(4)) and thyroid-stimulating hormone (TSH) at weeks 1, 2 and 4. In the XZ group, significant increase in thyroid weight and decrease in serum T(4) levels were observed at all time points. Serum T(3) and TSH levels were significantly decreased and increased, respectively, at week 1, but returned to within the control range thereafter. In Experiment III, male F344 rats received a diet containing 1000 or 0 p.p.m. XZ, they were examined for thyroid iodine uptake and organification of XZ after 1 and 2 weeks. The thyroidal iodine uptake per milligram of thyroid and the amount of iodine bound to 1 mg protein showed a tendency for decrease at week 1 and significant decrease at week 2. These results indicate that XZ has tumor-promoting effects on thyroid follicular cells, and suggest an involvement of alterations in thyroid-related hormone levels due to inhibition of thyroid iodine uptake and organification, resulting, provably, in serum TSH stimulation depending on continuous reduction of serum T(4) level through the feedback system in the pituitary-thyroid axis.     

Elevated oxidative stress and DNA damage and repair levels in urinary bladder carcinomas associated with schistosomiasis

To cast light on mechanisms underlying development of urothelial carcinomas (UCs) of the urinary bladder associated with Schistosomiasis, we immunohistochemically analyzed the relationship between oxidative stress markers, DNA single strand breaks (ssDNA) which could also measure the levels of base damage and apoptosis in DNA, and expression of DNA repair genes with levels of nitric oxide synthases in bladder carcinomas of Egyptian patients with or without Schistosoma hematobium infection. Marked elevation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels was found in squamous cell carcinomas and UCs associated with Schistosomiasis when compared with non-Schistosomal carcinomas. This was accompanied by strong over expression of the DNA-repair genes, 8-oxoguanine-DNA-glycosylase and apurinic/apyrimidinic endonuclease, as well as increased formation levels of ssDNA. Expression levels of inducible nitric oxide synthase (iNOS) which is known to be indirectly related to oxidative stress was higher in Schistosomal than in the non-Schistosomal carcinomas. However, expression of endothelial nitric oxide synthase was slightly stronger in non-Schistosomal than in the Schistosomal carcinomas. In conclusion, these findings suggest a strong correlation between Schistosoma haematobium infection and increased levels of oxidative stress accompanied by a continuous DNA damage and repair in UCs, all directly correlating with elevated iNOS.     

Effects of castration before and after treatment with N-bis (2-hydroxypropyl)-nitrosamine (DHPN) on the development of thyroid tumors in rats treated with DHPN followed by phenobarbital

The effect of castration on the development of thyroid tumors was studied histologically and biochemically in Wistar rats given a single ip injection of 210 mg of N-bis (2-hydroxypropyl)-nitrosamine (DHPN) followed by phenobarbital (Pb). Castration was performed one week after, or one week before the injection of DHPN. The injection of DHPN was given at the end of the first week, and the rats were fed 500 ppm Pb in the basal diet for 38 weeks from week 3 to week 40. The incidence of thyroid adenomas and cancers was 20% (4/20) and 10% (2/20) in rats treated with DHPN alone. It was 75% (15/20) and 40% (8/20) in rats treated with DHPN and Pb; 30% (6/20) and 15% (3/20) in rats treated with DHPN and Pb, and castrated after DHPN; 20% (4/20) and 0% in rats treated with DHPN and Pb, and castrated before DHPN and Pb; and 0% and 0% in rats castrated either before or after receiving DHPN. Castration thus inhibited the development of thyroid tumor in rats treated with DHPN. The inhibition of tumor development in rats treated with DHPN and Pb, and castrated before receiving DHPN, was greater than in the rats castrated after receiving DHPN. Castration inhibited the secretion of TSH in rats treated with DHPN and Pb.