Effect of gamma-ray irradiated poly(L-lactide) on the differentiation of mouse osteoblast-like MC3T3-E1 cells.

The purpose of this study was to clarify the effects of gamma-ray irradiated poly(L-lactide) (PLLA) on the proliferation and differentiation of mouse osteoblast-like MC3T3-E1 cells. The PLLA was y-irradiated at the dose of 10, 25 or 50 kGy, and the molecular weight of irradiated PLLA decreased with increasing irradiation dose. The proliferation and differentiation of MC3T3-E1 cells cultured on irradiated PLLA for 2 weeks were evaluated using micromass culture. The y-irradiation of PLLA did not affect the proliferation, but stimulated the differentiation of MC3T3-E1 cells cultured on irradiated PLLA. These results suggested that lower change in the molecular weight of PLLA was responsible for stimulation of the differentiation of MC3T3-E1 cells cultured on irradiated PLLA. Furthermore, the proliferation and calcification of MC3T3-E1 cells cultured in the medium containing low molecular weight PLLA for 2 weeks were evaluated. The low molecular weight PLLA also stimulated the calcification of MC3T3-E1 cells with no effect on the proliferation. The y-irradiation was suitable for PLLA on the differentiation of mouse osteoblasts.

Change in the particle size distribution of poly (L-lactide) wear debris by gamma-ray irradiation.

It has been known that the wear debris causes failure of implant prostheses. In this study, the convenient wear test of poly(L-lactide) (PLLA) was established and the particle size of PLLA wear debris was analyzed using the Coulter counter. Then, the changes in the particle size distribution of PLLA wear debris by gamma-ray irradiation were observed dose-dependently at the dose of 10, 25 and 50 kGy. With the increasing irradiation dose, the particle size distribution of PLLA wear debris shifted toward the smaller diameter size, and the mean diameter of PLLA wear debris significantly decreased. In addition, the tensile strength and the molecular weight of irradiated PLLA were also decreased by increasing the irradiation dose. The lowering of the molecular weight by gamma-irradiation resultingly caused the decreases in tensile strength of irradiated PLLA and the particle size of the wear debris derived from irradiated PLLA.

Toxicity study of a rubber antioxidant, mixture of 2-mercaptomethylbenzimidazoles, by repeated oral administration to rats.

2-Mercaptobenzimidazole (2-MBI), a rubber antioxidant, is known to exhibit potent antithyroid toxicity in rats and is a candidate as an environmental endocrine disrupter. 2-Mercaptomethylbenzimidazoles (a 1:1 mixture of 4-methyl and 5-methyl isomers, MMBIs), are also employed industrially as rubber antioxidants and are suspected to exert antithyroid toxicity such as 2-MBI. In this investigation, acute and subacute oral toxicity studies of MMBIs in Wistar rats were conducted. The clinical signs of acute oral toxicity were observed including decreased spontaneous movement, a paralytic gait, salivation and lacrimation, and adoption of prone and lateral positions. The LD50 was estimated to be 330 mg/kg. In the subacute oral toxicity study, male and female rats were treated with MMBIs by gavage at doses of 0 (corn oil), 4, 20 and 100 mg/kg for 28 consecutive days followed by a 2-week recovery period for the control and highest dose groups. Body weight and food consumption, clinical signs, organ weights, clinical biochemistry and haematological parameters including clotting times and micronuclei induction in bone marrow erythropoeitic cells, and histopathology were examined. Relative organ weights of lung, liver and kidney, and serum cholesterol and phospholipid significantly increased in male rats treated with MMBIs at doses of 20 and 100 mg/kg. Male rats administered 100 mg/kg MMBIs exhibited a 1.8-fold increase in thyroid weight associated with histopathological changes but not altered serum thyroid hormone levels. Female rats administered 100 mg MMBIs/kg exhibited significant increases of liver and kidney but not thyroid weights, and serum cholesterol level. The antithyroid toxicity of MMBIs in rats was estimated to be one-tenth that of 2-MBI. No-observed-effect levels for male and female rats were found to be 4 and 20 mg/kg, respectively, in this subacute oral toxicity study.

Toxicity study of a rubber antioxidant, 2-mercaptobenzimidazole, by repeated oral administration to rats.

The chemical structure of 2-mercaptobenzimidazole (2-MBI), which is widely used as a rubber antioxidant, is partially similar to those of thiourea (TU) and ethylenethiourea (ETU), both potent thyrotoxic compounds. In order to determine the oral toxicity of 2-MBI, a 28-day repeated dose toxicity study in Wistar rats followed by observation over a 14-day recovery period was conducted at dose levels of 2, 10 and 50 mg/kg 2-MBI administered by gavage. No toxic deaths occurred due to 2-MBI treatment. Decreases of body weight gain and food consumption in the 50 mg/kg dose group were observed during the second half of the treatment period. In addition, hematological examination and serum biochemical tests revealed decreased white blood cells and hemoglobin and increased serum urea nitrogen, cholesterol, phospholipid, gamma-glutamyl transpeptidase and the Na+/K+ ratio in the 50 mg/kg dose group. Marked thyroid enlargement (to 10 fold the control weight), histopathologically associated with diffuse hyperplasia of follicles with decreased colloid and thickening of the fibrous capsule, was found. Reduction in thymus weight was also observed in a dose-dependent manner, without significant histopathological alteration. The non-observed effect level (NOEL) of 2-MBI in this gavage study was found to be less than 2 mg/kg/day based on the significant decrease in thymus weight in the 2 mg/kg 2-MBI treatment group. In an ancillary study, measurement of serum levels of T3, T4 and TSH, and thyroid weight after gavage treatment with 0.15 and 0.3 mmol/kg of three antithyroid compounds for 14 days revealed a more potent antithyroid effect for 2-MBI than for TU or ETU.

[Twenty-eight days repeated dose toxicity test of N-(fluorodichloromethylthio)phthalimide in rats].

N-(Fluorodichloromethylthio)phthalimide (Fluor-folpet) has been widely used as an anti-mold and anti-bacterial agent. In this study, 28 days repeated-dose oral toxicity study of fluor-folpet was carried out in Slc:Wistar rats. An oral toxicity study for fluor-folpet, the twenty-eight days test, repeated-dose, oral administration, was performed as follows: Five week-old rats, male and female, 10 rats, each/group, were treated with intragastric administration of fluor-folpet with a dose of 0 (1% Sodium CMC, control), 20, 80 and 320 mg/kg, body weight. Recovery test, for 14 days after the last treatment, was examined for the control and the 320 mg/kg groups. The 320 mg/kg groups, both males and females, showed significantly reduced their body-weight gain compared with the control group. In the 320 mg/kg group, five out of 20 male rats and four out of 20 female rats died from dyspnea during the treatment period. In the female rats in the 320 mg/kg group, serum ChE level was decreased to 50% of control level and gamma-GT was increased in a dose-dependent manner, but these serum levels recovered after 14 days non-treatment period. No histopathological change, relating to the treatment, in liver was observed. Increased weight of the kidney and vacuolation in renal tubules were found in both sexes of 320 mg/kg group. Hyperkeratosis and hyperplasia of the stomach epithelium were observed at the dose more than 80 mg/kg in male, and more than 20 mg/kg in female. A supplemental study, repeated-dose, oral administration in rats carried out to examine the dyspnea revealed that severe acute toxic damages in epithelium of nasal cavity and meatus nasopharyngeus were induced by intragastric administration of fluor-folpet. Fluor-folpet is shown to be cytotoxic. In conclusion, the no-observed-effect level (NOEL) for fluor-folpet was not found under the experimental conditions employed in this repeated-dose toxicity study.

The effects of oligomers content and surface morphology on foreign-body tumorigenesis with polyetherurethanes: two years subcutaneous implantation study in rats.

Three polyurethane materials were prepared by removing and adding the leachable oligomers from and to the same polyetherurethane (PEU). The three PEU materials were dissolved in tetrahydrofuran (THF) and dimethyformamide (DMF) and the solutions were cast on a glass plate to make films of smooth and foamed surfaces, respectively. These six materials and polydimethylsioxane (silicone) were implanted into subcutaneous pocket of rats for 2 years to evaluate the long-term effects around the implant. Among the smooth surface implants, PEU materials induced a higher incidence of tissue responses, including tumor formation than silicone. However, no relationship between the oligomer content and the tissue responses was found. Changing surface morphology from a smooth to a foamed one prolonged the latent period of tumor development and decreased the total tumor incidence.

Identification of causative chemicals of allergic contact dermatitis using a combination of patch testing in patients and chemical analysis. Application to cases from rubber gloves.

5 cases of allergic contact dermatitis from rubber gloves were investigated by our recommended procedures using a combination of patch testing in patients and chemical analysis of causative rubber products by gas chromatography (GC) and high-performance liquid chromatography (HPLC). We previously confirmed that zinc ethylphenyldithiocarbamate (ZEPC), a dithiocarbamae-type accelerator (DTC), was causative in a case of allergic contact dermatitis from rubber work gloves. Subsequently, we have clarified that DTCs such as zinc dimethyldithiocarbamate (ZDMC), zinc diethyldithiocarbamate (ZDEC) and zinc dibutyldithiocarbamate (ZDBC) and amines such as dimethylamine (DMA), diethylamine (DEA) and piperidine (PIP) were also causative in cases from surgical rubber gloves. Thus, our investigative studies revealed that, although thiurams have been taken much more notice of as allergenic compounds than their corresponding DTCs and amines, not only DTCs such as ZDMC, ZDEC, ZDBC and ZEPC, but also amines such as DMA, DEA and PIP were noteworthy causative candidates of allergic contact dermatitis from rubber gloves.

[Subchronic toxicity study of tributoxyethyl phosphate in Wistar rats].

Tributoxyethyl phosphate (TBEP) is widely used in household materials such as plasticizer, floor polish and flame retardant in plastic resins and synthetic rubbers. This compound has been detected at ppb level in underground water. In order to elucidate the toxicity of TBEP, a 14-week oral toxicity study was conducted. Wistar rats (5-weeks old, male & female, 15 rats/group) were given diet containing 0, 0.03, 0.3 or 3.0% TBEP. Suppression of body weight gain was observed in both sexes of the 3.0% group. Serum cholinesterase activity was significantly decreased in both sexes of the 0.3 and 3.0% groups and serum gamma-glutamyl transferase activity was significantly increased in both sexes of the 3.0% group after 5 and 14 weeks exposure. Amylase in serum was also increased in 0.3 and 3.0% group males and 3.0% group females. Absolute and relative liver weights in both sexes were significantly increased in the 3.0% group after 5 and 14 weeks of exposure. Histopathological examination revealed moderate periportal hepatocyte swelling in male rats of the 3.0% group after 14 weeks exposure but this change was not found in male rats given 0.3% or less of TBEP in the diet or in any of the females. These findings indicated that the liver is a target organ for TBEP toxicity. We concluded a no-observed effect level (NOEL) of TBEP in the diet of 0.03% (male: 20 mg/kg/day, female: 22 mg/kg/day) under the conditions of this toxicity study.

Identification of causative chemicals of allergic contact dermatitis using a combination of patch testing in patients and chemical analysis. Application to cases from industrial rubber products.

3 cases of allergic contact dermatitis from industrial rubber products were investigated using a combination of patch testing in patients and chemical analysis of causative rubber products by gas chromatography (GC), GC-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). Our studies revealed N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), a typical rubber allergen, as a causative chemical in a case from a brand of heavy-duty rubber gloves and a case from a black rubber ring for car manufacture, and zinc ethylphenyldithiocarbamate (ZEPC), a dithiocarbamate (DTC)-type accelerator, as a causative chemical in a case from a brand of rubber work gloves: both IPPD and ZEPC, which showed positive patch test reactions, were confirmed in the extracts of the causative rubber products by GC, GC-MS and/or HPLC.

Identification of causative chemicals of allergic contact dermatitis using a combination of patch testing in patients and chemical analysis. Application to cases from rubber footwear.

5 cases of allergic contact dermatitis from rubber footwear were investigated by a combination of patch testing in patients and chemical analysis of causative rubber products. Our studies revealed 2-mercaptobenzothiazole (MBT) and benzothiazyl disulfide (MBTS) (typical allergenic accelerators) as causative chemicals in 3 cases from children's rubber shoes, ladies' rubber boots and ladies' canvas shoes. These 3 patients reacted to mercaptobenzothiazole-type accelerators including MBT and MBTS. MBT and MBTS were determined in each item of causative footwear by chemical analysis, including extraction by shaking with acetone-chloroform (1:1) mixture at room temperature and determination using reversed-phase high-performance liquid chromatography (RP-HPLC). Subsequently, we identified styrenated phenol (SP), a newly found allergenic antioxidant, as a causative chemical in a case from ladies' canvas shoes. The patient reacted to SP but not to MBT and MBTS, though SP, MBT and MBTS were determined in the causative shoes by gas chromatography (GC), GC-mass spectrometry (GC-MS) and HPLC. We also identified p-tert-butylphenol-formaldehyde resin (PTBP-F-R), (a known allergenic adhesive ingredient) as a causative chemical in a case from ladies' sneakers. The patient reacted to PTBP-F-R but not to p-tert-butylphenol (PTBP), MBT and MBTS. These 4 compounds were determined in the causative sneakers by GC, GC-MS and HPLC. Thus, our studies revealed that not only known allergens, such as MBT, MBTS and PTBP-F-R, but also a newly found one, such as SP, were important causes of allergic contact dermatitis from rubber footwear.

Phase studies of a urethane model compound and polyether macroglycols by infrared spectroscopy and the relationship between eutectic composition of soft segment and blood compatibility.

The binary mixtures of a urethane model compound, diethyl 4,4'-methylenebis(N-phenylcarbamate) (MDU), and various polyether macroglycols have been investigated mainly by infrared (IR) spectroscopy. The mixtures of macroglycol and MDU showed two C=O bands (free C=O at higher wave number, hydrogen bonded C=O at lower wave number), and the intensity of free C=O increased while that of hydrogen bonded C=O decreased linearly with increasing molar ratio of macroglycol/MDU. The slope of the increase or decrease suddenly changed at the specific molar ratio around the eutectic composition. The eutectic molar composition for PTMO1000/MDU was determined as 1.15 or 1.1 by differential scanning calorimetry (DSC) or infrared (IR) studies while that for PTMO3000/MDU as 0.345 or 0.55 by DSC or IR, respectively. The eutectic compositions for other sets were determined by IR studies as follows: PEO1000/MDU, 0.4; PEO3000/MDU, 0.16; PPO1000/MDU, 1.4; PPO3000/MDU, 0.45. The number of ethylene oxide, tetramethylene oxide, and propylene oxide units to form a eutectic with MDU calculated from these values were 15-20, 10-11, and 23-24, respectively. The similar DSC or IR changes were observed in the various kinds of polyurethanes such as MDI/BD, MDI/PTMO/BD, and MDI/PTMO polymers. The relationship between the eutectic compositions of soft segments (MDI/macroglycol) and the ideal Mn of the macroglycols in blood compatibility of segmented polyurethanes are discussed.