Biomechanical rationale for six splinted implants in bilateral canine, premolar, and molar regions in an edentulous maxilla.

PURPOSE: To determine the influence of number and location of implants loaded on the stress to the bone in an edentulous maxilla using a three-dimensional finite element model (3D FEM). MATERIAL AND METHODS: Computed tomographic data with the bone density of a dry skull were used to construct a 3D FEM. Titanium implants were simulated in the configuration as 14 unsplinted implants (US14), 14 splinted implants (S14), 6 splinted implants (canine, premolar, and molar regions, S6), 4 splinted implants (S4), and 6 anterior implants (incisors and canines, A6). Distributed loads of 200 N were applied on the occlusal table of the superstructures. RESULTS: The S6 model was subjected to a similar amount of stress and deformation to the US14 and the S14. The S4 and A6 models were subjected to approximately three times of stress under the vertical load, and approximately five times of stress under the inclined load, respectively, compared with the S6 model. CONCLUSIONS: The 3D FEM analyses suggest that the six splinted implants configuration has a similar stress and deformation pattern as compared with naturally positioned splinted 14 implants in the edentulous maxilla.

Concordance between Results of Medium-term Liver Carcinogenesis Bioassays and Long-term Findings for Carcinogenic 2-Nitropropane and Non-carcinogenic1-Nitropropane in F344 Rats.

This study was conducted to determine the concordance of results for a pair of structural isomers, 2-nitropropane (2-NP) and 1-nitropropane (1-NP), using the rat medium-term liver carcinogenesis bioassay (Ito test) and previously published long-term carcinogenicity tests. Male F344 rats were given a single intraperitoneal injection of DEN (200 mg/kg b.w.) to initiate hepatocarcinogenesis. After 2 weeks, they received per os 0, 0.8, 4 or 20 mg/kg/day of 2-NP or 1-NP six times a week and were subjected to two-thirds partial hepatectomy at week 3. Non-initiated groups receiving 0 or 20 mg/kg/day were also included. The animals were sacrificed for quantitative analysis of GST-P-positive foci at week 8. With the highest dose of 2-NP, significantly increased numbers and areas of GST-P-positive foci were demonstrated as compared with the respective control but were not noted with 1-NP. In the non-DEN-initiated groups, many small GST-P-positive foci of less than 0.2 mm in diameter were also induced in the rats treated with 2-NP at 20 mg/kg/day but were lacking with 1-NP. These results strongly support that 2-NP is a complete hepatocarcinogen with a potent initiation activity, whereas 1-NP is not.

Ninety-day oral toxicity study of rhamsan gum, a natural food thickener produced from Sphingomonas ATCC 31961, in Crl:CD(SD)IGS rats.

This study was designed to evaluate and characterize any subchronic toxicity of rhamsan gum, a polysaccharide produced from Sphingomonas strain ATCC 31961, when administered to both sexes of Crl:CD(SD)IGS rats at dietary levels of 0 (control), 0.5, 1.5, and 5.0% (10 rats/sex/group). During the study, the treatment had no adverse effects on clinical signs, survival, body weights and food and water consumption, or on findings of urinalysis, ophthalmology, hematology, or blood biochemistry. Examination of gross pathology and histopathology exhibited no differences of toxicological significance between control and treated rats. Increased relative cecum (filled) and cecum (empty) weights, evident in males of 1.5% group and both sexes of the 5.0% group, were considered to be a physiological adaptation. Thus, the results indicated the toxic level of rhamsan gum to be more than 5.0%, and the no-observed-adverse-effect level (NOAEL) was concluded to be 5.0% (3,362 mg/kg body weights/day for males, and 4,304 mg/kg body weights/day for males) from the present study.

A 28-day oral toxicity study of fermentation-derived cellulose, produced by Acetobacter aceti subspecies xylinum, in F344 rats.

This study was designed to evaluate any adverse effect of fermentation-derived cellulose, produced by Acetobacter aceti subspecies xylinum, when administered to both sexes of F344 rats at dietary levels of 0, 1.25, 2.5, and 5.0% for 28 days. The treatment had no adverse effects on clinical signs, mortality, body weights and food and water consumption, or on urinalysis, ophthalmology, hematology, blood biochemistry, and histopathology findings. At necropsy, slight increased absolute and relative cecum weights, evident in females ingesting 2.5% and 5.0% dietary levels, were considered to be a physiological adaptation to the poorly absorbed fermentation-derived cellulose. The non-observed-adverse-effect level (NOAEL) from the present study was concluded to be 5.0% in the diet (5,331 mg/kg body weights/day for males, and 5,230 mg/kg body weights/day for females).

Lack of carcinogenicity of L-isoleucine in F344/DuCrj rats.

The carcinogenic potential of L-isoleucine, used as a food fortifier, was examined in both sexes of F344 rats. Groups of 50 female and 50 male animals were given diet containing L-isoleucine at concentrations of 0%, 2.5% or 5.0%. No treatment-related changes in the survival rate, general condition, body weight, food consumption, urinalysis, hematology or clinical chemistry data and organ weights were noted. Detailed histopathological examination revealed no treatment-related increase in the incidences of any non-neoplastic or neoplastic lesions. The results indicate that L-isoleucine is not carcinogenic in F344 rats of either sex.

Lack of carcinogenicity of silicone resin (KS66) in F344 rats.

The carcinogenic potential of silicone resin (KS66), used as an antifoaming food additive, was examined in both sexes of F344 rats. Groups of 50 female and 50 male animals were given diet containing KS66 at doses of 0%, 1.25% and 5.0%. No treatment related effects were noted regarding survival rate, general condition, body weight, food consumption, hematology and organ weight data. Detailed histopathological examination revealed no treatment-related increase in the incidences of any non-neoplastic or neoplastic lesions. The results demonstrate that KS66 is not carcinogenic in F344 rats of either sex.

Lack of evidence for endocrine disrupting effects in rats exposed to fenitrothion in utero and from weaning to maturation.

Fenitrothion is a broad-spectrum organophosphate insecticide. Recently, it has been reported to exert androgenic or anti-androgenic activity in in vitro and in vivo screening assays, although the effects appear equivocal in vivo. To provide a conclusive and comprehensive evaluation of fenitrothion, especially regarding its anti-androgenic activity in the reproductive and endocrine systems, we conducted a one-generation reproductive toxicity study at appropriately toxic dose levels with a number of sensitive endpoints for endocrine disruption. Fenitrothion was administered to Crj:CD(SD)IGS parental animals (P) at concentrations of 10, 20, and 60 ppm in the diet for 10 weeks prior to mating, and throughout mating, gestation and lactation. Their offspring (F1) were exposed from weaning until maturation at the age of 10 weeks. In the P generation, brain cholinesterase activity was remarkably reduced in the 60 ppm males and in the 20 and 60 ppm females. Reproductive performance, organ weights, histopathology, and sperm analytical parameters were not affected. In the F1 generation, no general toxicity or effects on anogenital distance, retention of areolae/nipples, onset of puberty, organ weights, histopathological findings, and sperm parameters were observed. In conclusion, fenitrothion had no effects on the reproductive or endocrine systems of the P and F1 generations, even at toxic doses that markedly suppressed brain cholinesterase activity in P animals. The results suggest that fenitrothion at in-use levels in the environment is unlikely to cause disruption of human endocrine systems.

Effects of perinatal exposure to flutamide on sex hormone responsiveness in F1 male rats.

Pregnant rats were administered flutamide (0 and 10 mg/kg, p.o.) from gestation Day 14 to post-parturition Day 3 and effects on responsiveness to androgens (testosterone propionate, TP; dihydrotestosterone, DHT) in male offspring were examined with a Hershberger assay. Male pups of each group were assigned to 6 subgroups as follows: Group 1, castration and euthanized at postnatal Day 46 (PND 46); Group 2, castration + vehicle; Group 3, castration + TP; Group 4, castration + DHT; Group 5, vehicle; Group 6, DHT. After castrations were conducted at PND 36, animals were treated with TP (2 mg/kg in corn oil, s.c.) or DHT (1.25 mg/kg in corn oil, s.c.) once a day for 10 days, beginning at PND 46. At PND 56, the following organs/tissues were removed and weighed: ventral prostate, dorso-lateral prostate, seminal vesicles with coagulating glands, levator ani muscle plus bulbocavernosus muscle, Cowper's gland, and glands penis. Analysis of serum testosterone, LH and FSH in Groups 2, 3, 4, 5 and 6, and RT-PCR using prostate tissue from Groups 2, 3 and 4 were carried out. Perinatal exposure to flutamide caused decreased weights of androgen-dependent organs. Responses to androgens were recognized in organs of all castrated groups, with increased organ weights, especially in animals administered TP where values were essentially equal to or greater than those of intact animals in both the control and the 10 mg/kg group. On the other hand, the degree of weight increase of the ventral prostate and seminal vesicles with TP or DHT treatment in castrated animals was smaller in the flutamide administration group than in the controls. In hormone assays, castrated + vehicle animals showed higher serum LH than the other groups. Serum FSH was high in the castrated groups (Group 2>Group 4>Group 3), while in the noncastrated group a constant level was noted, with or without flutamide. No effect of flutamide administration was observed regarding sex hormone. RT-PCR using ventral prostate tissue revealed no significant differences in expression of AR, C3, VEGF, TGF-beta1, beta2, KGF and CK8 mRNA after androgen treatment between the control and flutamide treatment groups. C3 mRNA was increased in androgen-treated animals, whereas AR, TGF-beta and KGF mRNAs were decreased. Perinatal exposure to anti-androgen causes irreversible abnormalities in male pups. Concerning the responsiveness to TP and DHT, the degrees of weight changes in ventral prostate and seminal vesicles in castrated animals were decreased. However, the other organ weights, the sex hormone levels and androgen-reactive gene expression in the ventral prostate were not influenced by perinatal flutamide treatment in the present study.

Involvement of toxicity as an early event in urinary bladder carcinogenesis induced by phenethyl isothiocyanate, benzyl isothiocyanate, and analogues in F344 rats.

Phenethyl isothiocyanate (PEITC)(1) and benzyl isothiocyanate (BITC), naturally occurring constituents of cruciferous vegetables, have been reported to exert inhibitory effects against development of tobacco-specific carcinogen-induced lung tumors and are regarded as promising chemopreventive agents for lung cancer. However, tumor promoting and carcinogenic activities in the rat urinary bladder have been detected in several animal models. The purpose of the present study was to investigate early changes in rat urinary bladder epithelium induced by PEITC and BITC and to explore promotion/carcinogenic mechanisms. In the first experiment, in order to assess acute toxic effects, PEITC or BITC at 0.1% each in the diet were administered to 6-week-old F344 rats for 1, 2, 3, and 7 days and sequential histopathological assessment and urinalysis were performed. In the second and third experiments, structure-activity relationships of PEITC, BITC and 8 other analogues, benzyl isocyanate and benzyl thiocyanate, and phenyl-, alpha-naphthyl-, tert-butyl-, butyl-, methyl-, and ethyl isothiocyanates (ITCs) were explored in a 14-day experiment. In the first experiment, the urinary pH was significantly lowered on day 1 by both PEITC and BITC. Striking features of toxicity, such as marked inflammatory changes characterized by cellular infiltration, apoptosis/single cell necrosis, cytoplasmic vacuolation, erosion, and hemorrhage in the urinary bladder were caused, with peaks apparent on days 2 or 3, respectively. Sequential change in 5-bromo-2'-deoxyuridine (BrdU) labeling indices was in line with the inflammatory response, but the thickness of the urinary bladder epithelium continued to gradually increase up to day 7. In the second and third experiments, simple and papillary or nodular (PN) hyperplasias were observed after 14-days treatment with PEITC, BITC, and phenyl- and butyl ITCs. These results suggest that continuous urinary epithelial cell proliferation due to cytotoxicity may play an important role in the early stage of rat urinary bladder carcinogenesis due to oral administration of ITCs. In addition, hydrophobic activity of ITCs, dependent on the alkyl carbon chain length, might strongly influence the induction of bladder lesions in rats.

Four-week oral toxicity study of 1-carboxy-5,7-dibromo-6-hydroxy-2,3,4-trichloroxanthone (HXCA), an impurity of Phloxine B, in F344 rats.

This study was designed to evaluate and characterize any subacute toxicity of 1-carboxy-5,7-dibromo-6-hydroxy-2,3,4-trichloroxanthone (HXCA), an impurity of Phloxine B (Food Red No. 104 in Japan, D&C Red No. 28 in the USA), when administered to both sexes of F344 rats at dietary levels of 0 (control), 0.005, 0.05 and 0.5%. During the study, the treatment had no effects on clinical signs, survival, urinalysis or ophthalmology. Hematology, blood biochemistry, gross pathology, organ weights, organ to body weight ratios and histopathology exhibited no differences of toxicological significance between control and treated rats. Reactions to treatment may be summarized as follows: there was a tendency for increased food and water consumption and decreased food efficiency in both sexes of the 0.5% group. Thus, these results indicated the no-observed-adverse-effect level (NOAEL) of HXCA to be 0.05% (39.3 mg/kg/day for males, and 41.0 mg/kg/day for females).

Effects of antioxidant 1-O-hexyl-2,3,5-trimethylhydroquinone or ascorbic acid on carcinogenesis induced by administration of aminopyrine and sodium nitrite in a rat multi-organ carcinogenesis model.

The effect of antioxidant, 0.25% 1-O-hexyl-2,3,5-trimethylhydroquinone (HTHQ) or 0.25% ascorbic acid (AsA), on carcinogenesis induced by administration of 0.05% aminopyrine (AP) and 0.05% sodium nitrite (NaNO2), was examined using a rat multi-organ carcinogenesis model. Groups of twenty F344 male rats were treated sequentially with an initiation regimen of N-diethylnitrosamine, N-methyl-N-nitrosourea, N-butyl-N-(4-hydroxybutyl)nitrosamine, N,N'-dimethylhydrazine and 2,2'-dihydroxy-di-n-propylnitrosamine during the first 4 weeks, followed by AP+NaNO2, AP+NaNO2+HTHQ, AP+NaNO2+AsA, NaNO2+HTHQ, NaNO2+AsA, each of the individual chemicals alone or basal diet and tap water as a control. All surviving animals were killed at week 28, and major organs were examined histopathologically for development of preneoplastic and neoplastic lesions. In the AP+NaNO2 group, the incidences of hepatocellular adenomas and hemangiosarcomas were 95% and 35%, respectively. When HTHQ or AsA was simultaneously administered, the incidences decreased to 58% and 11%, or to 80% and 15%, respectively. On the other hand, in the AP+NaNO2 group and the NaNO2-alone group, when HTHQ, but not AsA, was simultaneously administered, the incidence of carcinomas in the forestomach significantly increased. The results suggest that HTHQ can prevent tumor production induced by AP and NaNO2 more effectively than AsA. On the other hand, an enhancing or possible carcinogenic effect of simultaneous administration of HTHQ and NaNO2 only on the forestomach is suggested, while simultaneous treatment with the same dose of AsA and NaNO2 may not be carcinogenic to the forestomach or other organs.

Suppression of lung metastasis by aspirin but not indomethacin in an in vivo model of chemically induced hepatocellular carcinoma.

To examine the effect of non-steroidal anti-inflammatory drugs on metastasis formation, aspirin (ASP, 0.5% in diet) and indomethacin (IM, 0.005% in drinking water) were applied to an in vivo highly metastatic rat hepatocellular carcinoma (HCC) model in F344 male rats. Administration for 8 weeks after induction of highly metastatic HCC by sequential treatment with diethylnitrosamine and N-nitrosomorpholine did not cause any significant change in survival rate or body weight. Multiplicity of HCC in the liver increased during ASP or IM treatment without any significant histological alteration. Although absent in the rats killed at the end of the period of carcinogen exposure, lung metastasis at the end of the experiment was found in 100%, 89% and 100% of rats in the control, ASP and IM groups, respectively. Degree of metastasis was classified into three groups according to the number of metastatic nodules, i.e., slight (1 - 5 nodules), moderate (6 - 50) and severe (more than 51), which amounted to 0%, 43% and 57% in the control group. ASP significantly reduced the degree of metastasis, the incidences being 33%, 44%, and 11%, respectively, whereas IM was without significant influence. Both agents suppressed cell proliferation in HCCs, without any alteration of pan-cadherin expression. However, expression in HCC of mRNAs for intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, both of which are considered to play key roles in attachment of cancer cells to the endothelium, was significantly suppressed by ASP. Thus, the present study demonstrated that ASP, but not IM, has the potential to inhibit lung metastasis of rat HCC in vivo, possibly via reduced attachment of tumor cells to the vascular endothelium. Moreover, these data indicate this in vivo model for induction of rat highly metastatic HCC to be a useful tool for the assessment of the efficacy of therapeutic treatments to block metastasis formation.

Effects of perinatal exposure to flutamide on sex hormones and androgen-dependent organs in F1 male rats.

Flutamide, which has antiandrogenic properties, was administered to pregnant rats, and effects on male offspring were examined. Crj: CD (SD) IGS (SPF) females were administered flutamide (0.15, 0.6, 2.5, 10.0, 100 mg/kg, p.o.) from gestation Day 14 to post parturition Day 3. The number of pups, body weights, clinical features, anogenital distance (AGD), nipple retention, testicular descent, and urogenital malformation in F1 males were examined. Hormone measurement, necropsy and histopathological examination were carried out at post-neonatal Day 4 (PND 4) and PND 60. Sperm analysis was also carried out at PND 60. Decrease in body weight was seen in the 100 mg/kg group and the AGD was decreased at 2.5 mg/kg and above. Retention of nipples, hypospadia, vaginal pouches, penis malformation, unilateral ectopic testis, and decrease of organ weights (prostate, seminal vesicles, levator ani muscle plus bulbocavernosus muscle, testis) were observed at 10 mg/kg and above. Testicular testosterone (T) was increased significantly with 100 mg/kg at PND 4 and tendencies for increase were observed in serum T, LH and FSH at 10 mg/kg and more at the same time point. In contrast, elevated levels of LH and FSH were seen with 100 mg/kg at PND 60. Histopathological examination revealed defects or hypoplastic changes of genital organs (> or = 10 mg/kg), squamous metaplasia (10 mg/kg) or mucification (100 mg/kg) of the urethral diverticulum epithelium and inflammation of genital organs (100 mg/kg). Though only undescended testes lacked spermatogenesis at 10 mg/kg, atrophic change of seminiferous tubules and azoospermia were observed in the 100 mg/kg group, despite testicular descent. Perinatal administration of flutamide affected F1 male rats at 2.5 mg/kg and above. In addition to urogenital malformation, 100 mg/kg flutamide caused high LH and FSH levels at PND 60. This study indicates that the most sensitive parameter is AGD, whereby reduction was observed at 2.5 mg/kg. A clear no-effect level (NOEL: 0.6 mg/kg) was obtained in this perinatal study of an antiandrogenic chemical.

Lack of enhancing effect of two Kampo medicines, Sho-saiko-to (TJ-9) and Sairei-to (TJ-114), on rat urinary bladder carcinogenesis initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine.

The modifying potential of two Kampo medicines (Japanese traditional herbal medicines), Sho-saiko-to (TJ-9) and Sairei-to (TJ-114), on urinary bladder carcinogenesis in male F344 rats initiated with N-butyl-N-(4-hydroxybutyl)- nitrosamine (BBN) was evaluated. Groups of 20 animals were given 0.05% BBN in their drinking water for 4 weeks and then 0.7 or 2.8% TJ-9, 0.9 or 3.6% TJ-114, or 3.0% sodium bicarbonate (NaHCO(3)) as a positive control substance in their diet for 32 weeks. All rats were killed after 36 weeks and examined histopathologically. No adverse effects of the test compounds were found in terms of survival, clinical sign, and body weight. Administration of 0.7 and 2.8% TJ-9 and 0.9 and 3.6% TJ-114 in the diet did not affect the incidences or extent of PN hyperplasia in the BBN-treated rats. Incidences and multiplicities of papillomas were also not affected in rats fed 0.7 or 2.8% TJ-9 and 0.9% TJ-114, while they were significantly decreased in animals given 3.6% TJ-114 in the diet. The results thus demonstrated that neither of the test chemicals exerted any promotional activity on urinary bladder carcinogenesis, in clear contrast to NaHCO(3). In addition, bladder carcinogenesis was reduced by 3.6% TJ-114 in the diet, under the present experimental conditions.