Time course observation of thyroid proliferative lesions and serum levels of related hormones in rats treated with kojic acid after DHPN initiation.

Time course changes in thyroid proliferative lesions as well as related hormone levels in the blood of male F344 rats given N-bis(2-hydroxypropyl)nitrosamine (DHPN: 2800 mg/kg body weight, single s.c. injection) as an initiation treatment followed by pulverized basal diet containing 0% (Group 2), 2% (Group 3) or 4% (Group 4) kojic acid (KA) were examined at Weeks 1, 2, 4, 8 and 12. As an untreated control group (Group 1), rats were given basal diet for 13 weeks and examined in the same manner. Serum T3/T4 levels in the DHPN + 2% KA and DHPN + 4% KA groups were significantly reduced as compared with the DHPN-alone group at each time point. Serum TSH levels in both DHPN + KA groups were significantly increased at each time point in a treatment period-dependent manner from Weeks 1 to 12, and the extent of elevation was more remarkable in the DHPN + 4% KA group. At Week 2, there were no statistically significant intergroup differences in liver T4-UDP-GT activities on a milligram microsomal protein basis. Histopathologically, no thyroid proliferative lesions were observed in the untreated control group or the DHPN-alone group. However, diffuse follicular cell hypertrophy and decreased colloid in the thyroid were apparent in all rats of the DHPN + KA groups at each time point. In addition, focal follicular cell hyperplasias and adenomas of the thyroid were observed at high incidence in the DHPN + 2% KA group from Week 4 and in the DHPN + 4% KA group from Week 8. Multiplicities of focal follicular cell hyperplasias and adenomas of the thyroid in the DHPN + 2% KA group were significantly greater than those in the DHPN + 4% KA group at Week 8. In the pituitary, an increase in the number of TSH producing cells with expanded cytoplasm was apparent from Weeks 4 to 12 in both DHPN + KA groups. These results strongly suggest that thyroid proliferative lesions were induced by KA administration due to continuous serum TSH stimulation through the negative feedback mechanism of the pituitary-thyroid axis, resulting from depression of serum T3 and T4.     

Inhibition of thyroid iodine uptake and organification in rats treated with kojic acid.

In order to elucidate the mechanisms of reduction of serum thyroid hormones caused by continuous administration of kojic acid (KA) and its thyroid tumor-promotion effects, male F344 rats were given pulverized basal diet containing 0.008%, 0.03%, 0.125%, 0.5%, or 2% KA for 4 weeks. As an untreated control group, additional rats were given basal diet alone for the same period. The thyroid 125I uptake was significantly decreased in the groups receiving 0.03% or more. In addition, significant reduction of organic formation of iodine and serum T3 and T4 levels were observed in the 2% KA group along with pronounced elevation of serum (TSH). Both absolute and relative thyroid weights were significantly increased in the groups receiving 0.5% of KA or more. Histopathologically, decreased colloid in the thyroid follicles and follicular cell hypertrophy in the thyroid were apparent at high incidences in the groups given 0.03% or more. In addition, thyroid capsular fibrosis was evident in all rats of the 2% KA group. In quantitative morphometrical analysis, the ratio of the area of follicular epithelial cells to the area of colloids was significantly increased in the groups given 0.03% KA or more. The results suggest that KA alteration of thyroid-related hormone levels in the 2% KA group are due to inhibition of iodide uptake and iodine organification in the thyroid, with tumor-promoting effects on development of thyroid proliferative lesions, probably secondary to prolonged serum TSH stimulation resulting from negative feedback through the pituitary-thyroid axis.     

Absence of in vivo genotoxic potential and tumor initiation activity of kojic acid in the rat thyroid

To clarify the in vivo genotoxic potential of kojic acid (KA), formation of DNA adducts and 8-hydroxy-deoxyguanosine (8-OHdG) in the thyroids of male rats subjected to dietary administration of 2% KA for 2 weeks were assessed by 32P-postlabeling analysis and with a high-performance liquid chromatography system coupled to an electrochemical detector (ECD), respectively. In addition, to investigate possible tumor initiation activity, male F344 rats were given diet containing 0, 0.02, 0.2 or 2% kojic acid for 8 weeks followed by administration of 0.1% sulfadimethoxine (SDM), a thyroid tumor promoter, in the drinking water for 23 weeks with a subsequent 13-week recovery period (two-stage thyroid tumorigenesis model). Rats given four times by s.c. injection of N-bis(2-hydroxypropyl)nitrosamine (DHPN; 700 mg/kg bw) during the initiation period followed by administration of 0.1% SDM and rats given diet containing 2% KA for the initial 8 weeks or for the entire 31 weeks of the experiment, or basal diet alone were provided as controls. DNA adducts were not formed, and the 8-OHdG level was not increased in the thyroids of rats given 2% KA for 2 weeks. In the two-stage thyroid tumorigenesis model, neither adenomas nor carcinomas were induced in the groups given 0, 0.02, 0.2 or 2% KA followed by 0.1% SDM administration, and incidences and multiplicities of focal follicular cell hyperplasias did not demonstrate any significant intergroup differences at the end of administration and recovery periods. In contrast, incidences and multiplicities of focal follicular cell hyperplasias, adenomas and carcinomas were all significantly increased in the DHPN + 0.1% SDM group. Although the incidences and multiplicities of focal follicular cell hyperplasias in the group given 2% KA for 31 weeks were greater than those in the 2% KA + 0.1% SDM group and an adenoma was observed in a rat at the end of the recovery period, no development of carcinomas was evident at either time point. No thyroid proliferative lesions were induced in the group given 2% KA for the initial 8 weeks only. The results of the present studies indicate that KA has neither in vivo genotoxic potential nor tumor initiation activity in the thyroid, and strongly suggest that the earlier observed thyroid tumorigenic activity of KA is attributable to a non-genotoxic mechanism.     

Promotion of thyroid carcinogenesis by para-aminobenzoic acid in rats initiated with N-bis(2-hydroxypropyl)nitrosamine.

Sulfonamide analogues of para-aminobenzoic acid (PABA), a precursor of folate synthesis, have beneficial effects as antifolate, but thyroid peroxidase inhibition has been reported as a side effect that results in promotion of rat thyroid carcinogenesis. In the present study, effects of PABA itself on F344 rat thyroid carcinogenesis after initiation with N-bis(2-hydroxypropyl)nitrosamine (DHPN) were evaluated. In experiment 1, rats in groups 1-4 received a single subcutaneous injection of DHPN at 2800 mg/kg, and groups 5 and 6 received vehicle saline alone. From 1 week after DHPN initiation, rats in groups 2, 3, 4, and 6 were fed basal diet containing 0.25%, 0.5%, 1.0%, and 1.0% PABA, respectively, for 40 weeks. Rats in groups 1 and 5 received basal diet alone throughout the experiment. The final incidence of thyroid follicular cell adenomas and adenocarcinomas was significantly (p < 0.05 or 0.01) increased in groups 3 and 4 as compared to group 1. No thyroid tumors were found in groups 5 and 6. In experiment 2, animals in group 1 were fed basal diet alone, while groups 2 and 3 were given 0.5% and 1.0% PABA in the diet, respectively, for 2 weeks. Thyroid weights in group 3, and serum thyroid stimulating hormone level and proliferative activity of follicular cells in groups 2 and 3 were significantly (p < 0.05 or 0.01) elevated. In addition, the serum thyroxine level in group 3 was significantly (p < 0.05) depressed. These results clearly indicate that PABA exerts promotion/progression effects on rat thyroid carcinogenesis as a result of hypothyroidism followed by negative-feedback via the thyroid-pituitary axis.     

Pronounced synergistic promotion of N-bis(2-hydroxypropyl)nitrosamine-initiated thyroid tumorigenesis in rats treated with excess soybean and iodine-deficient diets.

We have reported that excess soybean treatment and iodine deficiency synergistically interact, resulting in remarkable induction of thyroid hyperplasias in rats. In the present study, modifying effects of excess soybean and iodine-deficient diets were investigated in the post-initiation phase of N-bis(2-hydroxypropyl)nitrosamine [DHPN]-initiated thyroid tumorigenesis in rats. AIN-93G in which casein was replaced with gluten was used as a basal diet to avoid possible iodine contamination. In Experiment 1, F-344 rats of both sexes were sc injected with DHPN at a dose of 2800 mg/kg body weight and then fed a diet containing 0%, 0.8%, 4%, or 20% defatted soybean for 12 weeks, with proportional replacement of gluten by soybean flour. Although no thyroid proliferative lesions were found in any group, the absolute thyroid weights were significantly (p < 0.01) elevated with the 20% soybean treatment. In Experiment 2, after similar sc injection of DHPN, rats were fed a basal diet or a diet containing 20% soybean under iodine normal or deficient conditions for 12 weeks. Soybean feeding to both sexes under iodine deficient but not normal conditions dramatically enhanced the development of thyroid follicular adenomas (p < 0.01) and adenocarcinomas (p < 0.05), in good agreement with decrease in thyroxine and increase in thyroid-stimulating hormone. Thus co-exposure to excess soybean and iodine deficiency results in synergistic promotion of DHPN-initiated thyroid tumorigenesis in rats, of which mechanisms appear to primarily involve effects on serum hormone levels.     

Studies on the carcinogenicity of potassium iodide in F344 rats.

A chronic toxicity and carcinogenicity study, in which male and female F344/DuCrj rats were given potassium iodide (KI) in the drinking water at concentrations of 0, 10, 100 or 1000 ppm for 104 weeks, and a two-stage carcinogenicity study of application at 0 or 1000 ppm for 83 weeks following a single injection of N-bis(2-hydroxypropyl)nitrosamine (DHPN), were conducted. In the former, squamous cell carcinomas were induced in the salivary glands of the 1000 ppm group, but no tumors were observed in the thyroid. In the two-stage carcinogenicity study, thyroidal weights and the incidence of thyroid tumors derived from the follicular epithelium were significantly increased in the DHPN+KI as compared with the DHPN alone group. The results of our studies suggest that excess KI has a thyroid tumor-promoting effect, but KI per se does not induce thyroid tumors in rats. In the salivary gland, KI was suggested to have carcinogenic potential via an epigenetic mechanism, only active at a high dose.     

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.     

Studies on the mode of action for thyroid gland tumor promotion in rats by phenobarbital

A study was conducted to determine the mode of action for phenobarbital promotion of thyroid follicular cell neoplasia in rats using an initiation-promotion model established by Hiasa et al. (Y. Hiasa, Y. Kitahori, M. Ohshima, T. Fujita, T. Yuasa, N. Konishi, and A. Miyashiro, 1982a, Carcinogenesis 3, 1187-1190). Seven groups of Charles River Crl: CD(SD)BR rats (20/sex/group) were treated with either saline or 700 mg/kg DHPN [N-bis(2-hydroxypropyl)nitrosamine] administered subcutaneously once a week for 5 weeks (Initiation Phase) followed by 15 weeks of treatment with control diet or diets containing 500 ppm of phenobarbital (Promotion Phase). Groups of rats were also treated with L-thyroxine (50 micrograms/kg/day) in the diet to determine its effect on thyroid gland tumor promotion by phenobarbital. The incidence of thyroid follicular adenomas in DHPN male rats treated with phenobarbital was markedly increased [83% (15/18 rats)] as compared to rats receiving DHPN alone [37% (6/16 rats)]. Thyroxine treatment completely blocked the tumor promoting effect of phenobarbital in that the tumor incidence [25% (5/20 rats)] was reduced back to or somewhat less than that observed with DHPN alone. In female rats no tumors were observed with DHPN nor was a promoting effect of phenobarbital observed. These results demonstrate the potential for a microsomal enzyme inducer such as phenobarbital to alter the incidence of thyroid gland neoplasia in the male rat. The inhibitory effect of L-thyroxine on tumor promotion by phenobarbital supports the hypothesis that the promoting effect of phenobarbital is mediated via increased pituitary secretion of thyroid stimulating hormone as a compensatory response to the known effects of phenobarbital on peripheral thyroxine metabolism and excretion.     

Indomethacin induces small intestinal damage and inhibits amitrole-associated thyroid carcinogenesis in rats initiated with N-bis(2-hydroxypropyl)nitrosamine

Effects of intestinal damage on thyroid carcinogenesis due to amitrole (AT) were examined in F344 male rats initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). In experiment 1, rats were provided with diet containing 0.03% AT for 20 weeks after a single subcutaneous injection of DHPN (2800 mg/kg body weight), and concomitantly received 0.01% indomethacin (IM) in the diet to cause small intestinal damage or 1% dextran sodium sulfate (DSS) in the drinking water for induction of colitis following a schedule of intermittent 1-week administration and 1-week withdrawal for a total of 10 times. Groups without AT- and/or IM or DSS treatment were also included. Histopathological examination revealed significant reduction in the incidence and multiplicity of follicular cell adenomas and adenocarcinomas in the group concomitantly treated with IM, but no change in the DSS group, as compared with the AT alone group. In experiment 2, rats were similarly fed diet containing AT for 3 weeks with concomitant IM or DSS treatment after a DHPN initiation, and serum thyroid stimulating hormone levels were found to be significantly elevated only in the IM case. The increase in thyroid follicular cell proliferation due to AT was also clearly suppressed in the group concomitantly treated with IM. From these findings, IM-induced intestinal damage may inhibit thyroid carcinogeneisis in rats, although contributions of other factors, such as a direct inhibitory effect of IM to thyroid follicular cell proliferation cannot be ruled out.     

Prostaglandin synthases influence thyroid follicular cell proliferation but not carcinogenesis in rats initiated with N-bis(2-hydroxypropyl)nitrosamine

To clarify roles of prostaglandin synthases in rat thyroid follicular carcinogenesis, effects of an antithyroid agent, sulfadimethoxine (SDM), and two prostaglandin H synthase (COX) inhibitors, indomethacin and nimesulide, on prostaglandin synthase expression, follicular cell proliferation, and tumor induction in thyroids of rats with or without N-bis(2-hydroxypropyl)nitrosamine (DHPN) initiation were examined. In experiment 1, F344 male rats were allowed free access to drinking water containing SDM (0.1%), SDM + indomethacin (0.0025% in diet), or SDM + nimesulide (0.04% in diet) for 4 weeks. Both COX inhibitors suppressed goitrogenic activity of SDM, but they did not significantly affect microsomal prostaglandin E synthase-2 (mPGES-2) expression levels enhanced by SDM. In experiment 2, all rats received an injection of DHPN (2800 mg/kg body weight), and starting 1 week later, they were treated as in experiment 1 for 4 or 10 weeks. Cell proliferation was suppressed or showed a tendency for suppression by the COX inhibitors in the follicular preneoplastic/neoplastic lesions and surrounding parenchyma, and this was obviously thyroid stimulating hormone independent at least at week 4. However, neither of the COX inhibitors altered the incidence or multiplicity of preneoplastic/neoplastic lesions. Immunohistochemistry revealed significant reduction and elevation of COX-2 and mPGES-2 expression, respectively, in the lesions, but these were also not changed by the COX inhibitors. These results suggest that COX-2 and PGES, and in turn PGE(2), might play important roles in follicular cell proliferation but do not affect tumor induction in this rat thyroid carcinogenesis model. Further studies are needed to clarify the significance of the reduction of COX-2 expression in preneoplastic/neoplastic lesions.     

Liver tumor promoting effect of etofenprox in rats and its possible mechanism of action

To investigate the liver tumor-promoting effects of etofenprox (ETF), a pyrethroid-like insecticide, 6 week-old male F344 rats were given an intraperitoneal injection of N-diethylnitrosamine (DEN). After 2 weeks from the DEN treatment, 12 rats per group received a powdered diet containing 0, 0.25, 0.50, or 1.0% ETF for 8 weeks. At the time of 2nd week of ETF administration, all animals were subjected to two-thirds partial hepatectomy (PH). One rat per group except for the 0.25% ETF group died due to surgical operation of PH. The number and area of glutathione S-transferase placental form (GST-P) positive foci significantly increased in the livers of DEN-initiated rats given 0.50% and 1.0% ETF compared with the DEN-alone group. Quantitative real-time RT-PCR analysis revealed that the mRNA expression of phase I enzymes Cyp2b1/2, phase II enzymes such as Akr7a3, Gsta5, Ugt1a6, Nqo1 significantly increased in the DEN+ETF groups. The immunohistochemistry showed the translocation of CAR from the cytoplasm to the nuclei of hepatocytes in the ETF-treated groups. Reactive oxygen species (ROS) production increased in microsomes isolated from the livers of ETF-treated rats, and thiobarbituric acid-reactive substances (TBARS) levels and 8- hydroxy-2-deoxyguanosine (8-OHdG) content significantly increased in all of the ETF-treated groups and DEN+1.0% ETF group, respectively. The results of the present study indicate that ETF has a liver tumor-promoting activity in rats, and suggest that ETF activates the constitutive active/androstane receptor (CAR) and enhances microsomal ROS production, resulting in the upregulation of Nrf2 gene batteries; such an oxidative stress subsequently induces liver tumor-promoting effects by increased cellular proliferation.     

Dose-threshold for thyroid tumor-promoting effects of xylazine in rats

To clarify the threshold dose of thyroid tumor-promoting effects of xylazine hydrochloride (XZ), male F344 rats received pulverized basal diet containing 0, 250, 500, or 1000 ppm XZ for 26 weeks with or without initiation of 2400 mg/kg N-bis(2-hydroxypropyl)nitrosamine (DHPN). Thyroid weights significantly increased in the groups with or without DHPN initiation that were given 500 ppm XZ or more. The serum thyroxine (T4) and triiodothyronine (T3) levels decreased significantly in the XZ 250 and XZ 1000 ppm groups, respectively, although there were no remarkable changes in the serum thyroid-stimulating hormone (TSH) levels. Histopathologically, follicular cell hyperplasias and adenomas were induced in the DHPN-alone and DHPN+XZ groups, and the incidences and multiplicities of these lesions in the DHPN groups treated with 500 ppm XZ or more were significantly higher than those in the DHPN alone group. These results suggest that the threshold dose of rat thyroid tumor-promoting effects of XZ is between 250 and 500 ppm under the present experimental condition.     

Effects of kojic acid on thyroidal functions in rats by single-dose administration and in cultured rat thyroid cells (FRTL-5 cells)

The effects of kojic acid (KA) on thyroidal function were studied by single-dose administration in rats and in cultured rat thyroid cells (FRTL-5 cells). In rats receiving a single dose of 1,000 mg/kg KA orally, the 125I uptake from blood into the thyroid gland was significantly lower than that of the control group from 30 min to 24 hr after administration. The 125I organification activity of the KA groups was significantly lower than control from 30 min to 6 hr after administration. However, the 125I organification activity at 24 hr or 48 hr after administration recovered enough to be nearly comparable with the control group. In the study in FRTL-5 cells, KA inhibited iodine organification dose-dependently, but did not inhibit iodine uptake. These results suggest that the observed lower iodine uptake activity in the single-dose administration study in rats was due to the inhibition of iodine organification caused by the oral administration of KA, consequently decreasing iodine in the entire thyroid gland. Although serum T4 showed a tendency to decrease from 2 hr to 48 hr after administration of KA, serum TSH did not show any evident change associated with KA in the single-dose administration study in rats. Based on these results, it is presumed that a massive dose or long administration period might be needed to decrease serum T4 and increase serum TSH. From these results, it is presumed that KA affected thyroidal function when given at a massive dose or in a long administration period by inhibiting iodine organification in the thyroid.     

Induction of altered hepatic foci by a mixture of dioxin-like compounds with and without 2,2',4,4',5,5'-hexachlorobiphenyl in female Sprague-Dawley rats

The hepatic tumor-promoting activity of a mixture of polyhalogenated aromatic hydrocarbons (PHAHs) was studied in a medium term two-stage initiation/promotion bioassay in female Sprague-Dawley rats. The PHAH mixture contained 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1, 2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,4,7, 8-pentachlorodibenzofuran (PeCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 2,3',4,4',5-pentachlorobiphenyl (PCB 118), 2,3,3',4,4', 5-hexachlorobiphenyl (PCB 156), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) and covered >90% of the total toxic equivalents (TEQ) present in Baltic herring. To determine possible interactive effects of di-ortho-substituted PCBs, the PHAH mixture was tested with (PHAH+) and without (PHAH-) PCB 153. Rats were initiated by a diethylnitrosamine injection (30 mg/kg body wt i.p.) 24 h after a partial 23 hepatectomy. Six weeks after initiation, the PHAH mixtures were administered once a week by subcutaneous injections for 20 weeks. Treatment with the PHAH mixtures caused liver enlargement and an increased activity of the hepatic cytochrome P4501A1/2 and P4502B1/2. All PHAH exposure groups exhibited an increased occurrence of hepatic foci positive for the placental form of glutathione-S-transferase. In the PHAH-group dosed 1 microgram TEQ/kg body wt/week, the volume fraction of the liver occupied by foci was significantly lower compared to the TEQ equivalent dosed TCDD group (3.8 vs 8.7%). The volume fraction was significantly increased in the groups treated with 0.5, 1, or 2 micrograms TEQ/kg body wt/week of the PHAH+ mixture (4.5, 5.2, and 6.6%, respectively) compared to the corn oil group (2.0%), but to a lower extent than expected on basis of the TEQ doses. Overall, the TEQ-based administered dose overestimated the observed tumor-promoting effects of this PHAH mixture. The applicability of the toxic equivalency factor concept, the role of differences in toxicokinetic properties and interactive effects of PCB 153 on hepatic deposition of the dioxin-like congeners are discussed.     

Concurrent administration of ascorbic acid enhances liver tumor-promoting activity of kojic acid in rats

We previously found that administration of ascorbic acid (AA) enhances the liver tumor-promoting activity of kojic acid (KA) in mice. To examine the reproducibility of these results in rats and the underlying mechanism of this effect, we employed a two-stage liver carcinogenesis model using male F344 rats. Two weeks after initiation with diethylnitrosamine (DEN), the animals received a diet containing 2% KA and drinking water with or without 5,000 ppm AA for a period of 7 weeks. A DEN-alone group was also established as a control. One week after the commencement of the administration, the animals were subjected to two-thirds partial hepatectomy. At the end of the experiment, the livers were analyzed immunohistochemically, and the mRNA expression level and extent of lipid peroxidation were measured. AA treatment enhanced the KA-induced tumor-promoting activity in terms of the number and area of liver cell foci that were positive for glutathione-S-transferase placental form. AA coadministration increased the number of hepatocytes positive for proliferating cell nuclear antigen and inversely decreased the number of TUNEL-positive cells. However, the increased level of thiobarbituric acid reactive substances resulting from KA treatment was suppressed by coadministration of AA. Gene expression analyses using low-density microarrays and real-time RT-PCR showed that coadministration of AA resulted in upregulation of genes related to cell proliferation and downregulation of those involved in apoptosis and/or cell cycle arrest. These results indicate that the concerted effects of AA on cell proliferation and apoptosis/cell cycle arrest probably through its antioxidant activity are involved in this enhancement.     

胰淀素对类固醇性骨质疏松大鼠骨代谢生化指标的影响

目的探讨胰淀素对类固醇性骨质疏松大鼠骨代谢生化指标的影响。方法采用3月龄雌性Wistar大鼠地塞米松肌肉注射法建立类固醇性骨质疏松症动物模型,随机将32只分为:正常对照组、模型组、胰淀素治疗组、维生素D组,每组8只。12周后行骨密度及血尿生化检查。结果①骨密度:与模型组相比,胰淀素治疗组腰椎骨密度增加35%,股骨骨密度增加17%,其效果优于维生素D;②生化指标:胰淀素治疗组骨钙素、骨碱性磷酸酶明显升高,同时尿羟脯氨酸/肌酐、尿1型胶原羧基末端肽/肌酐、尿钙/肌酐、尿磷/肌酐均普遍降低。结论胰淀素可以有效地阻止糖皮质激素性骨质疏松大鼠的骨量丢失,不仅可以促进骨形成,同时还具有抑制骨吸收的作用。     

Lack of modifying effects of atrazine and/or tamoxifen on thyroid carcinogenesis in rats pretreated with N-bis(2-hydroxypropyl)nitrosamine (DHPN)

The modifying effects of atrazine, and/or tamoxifen, on thyroid carcinogenesis were investigated in a rat two-stage carcinogenesis model following N-bis(2-hydroxypropyl)nitrosamine (DHPN) initiation. Five-week-old male F344 rats were given a single subcutaneous injection of DHPN (2800 mg/kg, body weight) or vehicle alone. Starting 1 week later, the animals were fed a diet supplemented with 0, 5, 50 or 500 ppm of atrazine, 500 ppm atrazine plus 5 ppm tamoxifen, or 5 ppm tamoxifen in the DHPN-treated groups, and 0 or 500 ppm of atrazine in the DHPN-untreated groups for 24 weeks. At autopsy major organs, including the thyroid, pituitary, liver, kidney, testis, epididymis, and brain, were collected and histopathologically examined. Body weights were significantly (P<0.05) decreased by the high doses of atrazine or tamoxifen, the effect being enhanced in combination. Relative thyroid weights were significantly increased (P<0.05) only in the tamoxifen-treated group and pituitary weights were elevated with 500 ppm atrazine plus tamoxifen (P<0.05). Relative liver weights were increased by the high dose of atrazine. However, the atrazine and/or tamoxifen treatments did not induce significant histopathological changes in the major organs, including the thyroid, nor cause significant changes in serum TSH levels. These results suggest that neither atrazine nor tamoxifen may promote thyroid carcinogenesis, alone as well as in combination.     

Chronic dietary toxicity and carcinogenicity study with potassium perfluorooctanesulfonate in Sprague Dawley rats

To investigate toxicity and neoplastic potential from chronic exposure to perfluorooctanesulfonate (PFOS), a two-year toxicity and cancer bioassay was conducted with potassium PFOS (K? PFOS) in male and female Sprague Dawley rats via dietary exposure at nominal K? PFOS concentrations of 0, 0.5, 2, 5, and 20 μg/g (ppm) diet for up to 104 weeks. Additional groups were fed 20 ppm for the first 52 weeks, after which they were fed control diet through study termination (20 ppm Recovery groups). Scheduled interim sacrifices occurred on Weeks 4, 14, and 53, with terminal sacrifice between Weeks 103 and 106. K? PFOS appeared to be well-tolerated, with some reductions in body weight occurring in treated rats relative to controls over certain study periods. Male rats experienced a statistically significant decreased trend in mortality with significantly increased survival to term at the two highest treatment levels. Decreased serum total cholesterol, especially in males, and increased serum urea nitrogen were consistent clinical chemistry observations that were clearly related to treatment. The principal non-neoplastic effect associated with K? PFOS exposure was in livers of males and females and included hepatocellular hypertrophy, with proliferation of endoplasmic reticulum, vacuolation, and increased eosinophilic granulation of the cytoplasm. Statistically significant increases in hepatocellular adenoma were observed in males (p=0.046) and females (p=0.039) of the 20 ppm treatment group, and all of these tumors were observed in rats surviving to terminal sacrifice. The only hepatocellular carcinoma observed was in a 20 ppm dose group female. There were no treatment-related findings for thyroid tissue in rats fed K? PFOS through study termination; however, male rats in the 20 ppm Recovery group had statistically significantly increased thyroid follicular cell adenoma, which was considered spurious. There was no evidence of kidney or bladder effects. In rats, the dietary dose estimated as the lower 95% confidence limit of the benchmark dose for a 10% increase in hepatic tumors was 8 ppm for both sexes. Recent mechanistic studies suggest a PPARα/CAR/PXR-mediated mode of action for the liver tumors observed in the present two-year study.     

Lack of modifying effects of atrazine and/or tamoxifen on thyroid carcinogenesis in rats pretreated with N-bis(2-hydroxypropyl)nitrosamine (DHPN).

The modifying effects of atrazine, and/or tamoxifen, on thyroid carcinogenesis were investigated in a rat two-stage carcinogenesis model following N-bis(2-hydroxypropyl)nitrosamine (DHPN) initiation. Five-week-old male F344 rats were given a single subcutaneous injection of DHPN (2800 mg/kg, body weight) or vehicle alone. Starting 1 week later, the animals were fed a diet supplemented with 0, 5, 50 or 500 ppm of atrazine, 500 ppm atrazine plus 5 ppm tamoxifen, or 5 ppm tamoxifen in the DHPN-treated groups, and 0 or 500 ppm of atrazine in the DHPN-untreated groups for 24 weeks. At autopsy major organs, including the thyroid, pituitary, liver, kidney, testis, epididymis, and brain, were collected and histopathologically examined. Body weights were significantly (P<0.05) decreased by the high doses of atrazine or tamoxifen, the effect being enhanced in combination. Relative thyroid weights were significantly increased (P<0.05) only in the tamoxifen-treated group and pituitary weights were elevated with 500 ppm atrazine plus tamoxifen (P<0.05). Relative liver weights were increased by the high dose of atrazine. However, the atrazine and/or tamoxifen treatments did not induce significant histopathological changes in the major organs, including the thyroid, nor cause significant changes in serum TSH levels. These results suggest that neither atrazine nor tamoxifen may promote thyroid carcinogenesis, alone as well as in combination.     

依那西普对类风湿关节炎患者骨代谢生化指标、骨密度的影响

目的:研究类风湿关节炎患者接受依那西普(etanercept,ETN)治疗52周后血清骨代谢生化指标、骨密度改变。方法:39例患者分为对照组(MTX7.5 mg/周逐渐加量至15 mg/周,3例患者于第8周时最大剂量为20 mg/周);治疗组17例(MTX用法同前,其中2例患者于第8周时最大剂量为20 mg/周,ETN:25 mg,每周2次,皮下注射)。于治疗前、12周、26周、52周分别检测骨保护素(OPG)、血清骨钙素(OC)、降钙素(CT)、甲状腺旁素(iPTH)。并行腰椎及股骨不同部位骨密度(BMD)测定。结果:2组在治疗前血清OPG水平即有显著降低,对照组随着治疗时间的持续而进一步降低。治疗组在治疗26周后出现升高,2组比较有统计学差异(P<0.01);而血清iPTH在治疗前2组均有显著升高,对照组随着治疗时间的持续而进一步升高。治疗组在治疗12周后出现升高,2组比较有统计学差异(P<0.01);2组患者腰椎、股骨颈、股骨沃德三角BMD比较有统计学意义(P<0.01)。结论:应用依那西普治疗类风湿关节炎能减少骨丢失、有效改善患者骨质疏松。