C_3H非自发性小鼠乳腺癌模型的建立

目的建立C3H非自发性小鼠乳腺癌模型。方法采用肿瘤组织块接种法和肿瘤细胞悬液接种法,将C3H自发性乳腺癌进行同种移植及异种移植,观察肿瘤生长情况,并连续传代。切除肿块作病理切片,免疫组化法检测雌激素受体(ER)、孕激素受体(PR)。结果>1 mm3体积的瘤块或>1×106细胞悬液移植接种,在接种后6~9 d在局部形成瘤性结节,继之迅速增大,成瘤率为100%;<0.5 mm3的瘤块和<0.5×106个细胞接种的成瘤率分别为40%和50%。肿瘤模型连续传代18代,生长稳定,传代周期固定。病理学检查为浸润性导管癌,ER阳性、PR阳性。结论该法建立的肿瘤模型,接种成功率高,成瘤时间周期短,适用于大面积的抗肿瘤药物实验。     

TLR4对MHV-3诱导的C3H／He小鼠病毒性肝炎转归的影响

目的探讨TLR4对3型鼠肝炎病毒（MHV-3）诱导的C3H／He小鼠肝炎转归的影响。方法观察C3H／HeJ及C3H／HeN小鼠感染MHV-3后的临床症状（皮毛异常、呼吸加快及身体颤抖）并进行评分。记录两亚系小鼠的存活情况并进行比较。所有小鼠观察至感染后40d。结果小鼠品系对临床症状评分不起作用（P=0．718）。临床评分有随时间变化的趋势（P〈0．001）,且时间因素的作用随小鼠品系而不同（P=0．004）。C3H／HeJ及C3H／HeN小鼠临床症状评分仅在感染后第5、6、13天出现差异：（13．071±1．184）和（10．933±4．608）（P〈0．001）,（8．321±5．048）和（11．304±3．901）（P〈0．001）,（13．091±1．578）和（10．846±3．671）（P=0．015）。C3H／HeJ及C3H／HeN小鼠存活率分别为26．7％和23．3％,平均存活时间分别为16．267d和16．433d,无显著差异（P=0．922）。结论MHV-3诱导的C3H／He小鼠病毒性肝炎转归不依赖于TLR4。     

硫酸乙酰肝素蛋白聚糖对C_3H小鼠乳腺癌移植瘤的抑制作用及其机制

目的观察硫酸乙酰肝素蛋白聚糖(HSPG)对C3H小鼠乳腺癌移植瘤的抑制作用及其机制。方法建立肿瘤模型并随机分为5组:生理盐水组、HSPG组(5、10、50mg.kg-1)及阳性对照组,各组动物自模型建立d2开始腹腔注射给药治疗22d并观察记录肿瘤体积。d24处死动物,称量肿瘤重量,计算胸腺指数及脾指数,使用原位凋亡检测法(TUNEL)检测HSPG对肿瘤细胞凋亡的影响,免疫组化检测血管内皮生长因子(VEGF)的表达。结果HSPG可明显抑制肿瘤生长,而不降低胸腺指数和脾指数。TUNEL结果HSPG组肿瘤组织中出现大量蓝黑色凋亡细胞,且明显多于生理盐水组,HSPG组肿瘤组织的VEGF的表达明显降低。结论HSPG对C3H小鼠移植性乳腺癌生长具有明显的抑制作用,其机制可能与诱导肿瘤细胞凋亡及抑制VEGF表达有关。     

Role of interferon in the resistance of C3H/HeJ mice to infection with herpes simplex virus

C3H/HeJ mice known to be defective in their responses to bacterial lipopolysaccharides, are more resistant to infection with herpes simplex virus (HSV) than the closely related strain C3HeB/FeJ. The increased resistance is reflected in higher early local interferon titers after HSV infection. However, NK cell activation by HSV is not correlated with resistance, since the NK cell response of C3H/HeJ mice was significantly lower than that of the control strain.     

Autoradiographic localization of 2-[I]iodomelatonin binding sites in the brains of C3H/HeN and C57BL/6J strains of mice

The present study uses in vitro autoradiography to localize 2-[¹²⁵I]iodemelatonin binding sites in the brain of two strains of mice, the C3H/HeN and the C57BL/6J, which have been shown to exhibit differences in pineal melatonin content. We found a differential pattern of distribution of 2-[¹²⁵I]iodomelatonin binding sites between the two strains with the suprachiasmatic nucleus, paraventricular nucleus of the thalamus, regions labelled in both strains. These studies should help to interpret behavioral changes due to activation of melatonin receptors in these strains of mice.     

Toxicokinetics of acrylamide and glycidamide in B6C3F1 mice

Acrylamide (AA) is a widely studied industrial chemical that is neurotoxic, mutagenic to somatic and germ cells, and carcinogenic in rodents. The recent discovery of AA at ppm levels in a wide variety of commonly consumed foods has energized research efforts worldwide to define toxic mechanisms, particularly toxicokinetics and bioavailability. This study compares the toxicokinetics of AA and its epoxide metabolite glycidamide (GA) in serum and tissues of male and female B6C3F1 mice following acute dosing by intravenous, gavage, and dietary routes at 0.1 mg/kg AA or intravenous and gavage dosing with an equimolar amount of GA. AA was rapidly absorbed from oral dosing, was widely distributed to tissues, was efficiently converted to GA, and increased levels of GA-DNA adducts were observed in liver after complete elimination from serum. GA dosing also resulted in rapid absorption, wide distribution to tissues, and produced liver DNA adduct levels that were approximately 40% higher than those from an equimolar dose of AA. While oral administration was found to attenuate AA bioavailability to 23% from the diet and to 32-52% from aqueous gavage, a first-pass effect or other kinetic change resulted in higher relative internal exposure to GA when compared to the intravenous route. A similar effect on relative GA exposure was also evident as the administered dose was reduced, which suggests that as dosing rate decreases, the conversion of AA to GA is more efficient. These findings are critical to the assessment of genotoxicity of AA at low doses in the food supply, which appears to depend on total exposure to GA.     

砒石对哮喘小鼠肺组织白三烯含量的影响

目的探讨砒石对哮喘小鼠的治疗作用及对肺组织LTB4、LTC4水平的影响。方法建立小鼠卵蛋白哮喘模型,灌胃给予砒石等药,对肺泡灌洗液进行白细胞分类计数,肺组织切片HE染色观察病理变化,用ELISA法检测肺组织匀浆LTB4、LTC4含量。结果哮喘组小鼠肺组织匀浆中LTB4、LTC4含量较生理盐水对照组升高。砒石1.25mg/kg能降低哮喘小鼠肺组织LTB4的含量;砒石0.625mg/kg可降低哮喘小鼠肺组织中LTC4水平至正常。砒石不能影响哮喘小鼠肺泡灌洗液中白细胞分类百分比。结论肺组织中LTB4、LTC4水平的增高可能在哮喘的发病中起作用。砒石能减轻哮喘小鼠肺的病理损害,降低哮喘小鼠肺组织LTB4、LTC4水平,从而表现出抗哮喘的活性。     

Effects of prenatal ethanol exposure in C57BL mice on locomotor activity and passive avoidance behavior

The purpose of this study was to examine the long-term behavioral effects of prenatal ethanol exposure in C57BL mice. Pregnant mice received free access to a liquid diet containing 25% ethanol-derived calories (EDC) from gestation days 6 to 18. Control animals were pair-fed an isocaloric 0% EDC diet during the same period of time. An additional control group was included that was maintained on standard lab chow and water throughout pregnancy. At 30 days of age, female offspring were tested for spontaneous locomotor activity in an open field under two lighting conditions (dim or bright illumination). Male off-spring were tested in a passive avoidance task at 25 days of age. The activity results demonstrated that the 25% EDC female progeny were more active than controls. This hyperactivity was observed under both lighting conditions, despite the fact that all groups evidenced suppressed activity when tested under bright lights. With regard to passive avoidance behavior, male EtOH-exposed offspring required a greater number of trials to reach criterion than controls. Additionally, they exhibited shorter latencies to enter the shock-associated chamber after receiving a single shock. Taken together, these results confirm our previous findings and demonstrate that C57BL mice are sensitive to both the deleterious behavioral and morphological consequences of prenatal ethanol exposure.     

Sustained induction of hepatic xenobiotic metabolising enzyme activities by phenobarbitone in C3H/He mice: relevance to nodule formation

Phenobarbitone (PB) was administered to male C3H/He mice at a dose of 85 mg/kg/day in a semisynthetic diet for up to 90 weeks. Throughout the treatment period a sustained induction of a number of parameters of hepatic Phase I and Phase II xenobiotic metabolism was observed. Histological examination revealed hypertrophy of the centrilobular cells of the liver lobule in PB treated mice and after 25 weeks small basophilic nodules were found in control and PB treated animals. In addition eosinophilic nodules, which were often large, developed in PB treated mice. Xenobiotic metabolising enzyme activities in large excised nodules after 70 or 90 weeks of PB treatment were either similar to or greater than those present in surrounding host tissue. Both phenobarbitone- and polycyclic hydrocarbon-type mixed function oxidase enzyme activities were induced in large nodules. In conclusion, PB produced a sustained induction of xenobiotic metabolising enzymes both in host tissue and in large eosinophilic nodules. The formation of these nodules in C3H/He mice was thus not associated with any failure of induction of hepatic xenobiotic metabolism.     

Prenatal alcohol exposure causes the over-expression of DHAND and EHAND by increasing histone H3K14 acetylation in C57 BL/6 mice

Prenatal alcohol exposure leads to congenital heart abnormal development, its mechanisms are still unknown. Recent reports have associated alcohol exposure with histone H3 acetylation. In the present study, we have performed the experiments to test the hypothesis that histone H3K14 acetylation is the key role in the fetal heart leads to over-expression of cardiac specific genes DHAND and EHAND caused by prenatal alcohol exposure. Seventy pregnant C57BL/6 mice were divided randomly into seven groups (n = 10). They were the untreated group, dimethyl sulfoxide group, alcohol exposure group, curcumin treatment group, both alcohol and curcumin treatment group, SAHA treatment group, both alcohol and SAHA treatment group. Fetal mouse hearts were collected on embryonic day 14.5. The changes of HATs activities, the acetylation levels of histone H3K14 (H3K14ac), the expression levels of cardiac specific genes DHAND and EHAND, and structure of chromatin were determined. Our data indicates that curcumin and SAHA significantly reduces and increases the activities of HATs and the levels of histone H3K14ac in fetal hearts, respectively. The expression of DHAND and EHAND is significantly down-regulated and up-regulated in the groups treated with curcumin and SAHA. Furthermore, our results from ChIP assays have shown that the histone H3K14ac connects with the DHAND and EHAND genes are significantly inhibited by curcumin and simulated by SAHA. Our study suggests that prenatal alcohol exposure causes the over-expression of DHAND and EHAND by increasing H3K14ac in mice.     

Immunohistochemistry of γ‐H2AX as a method of early detection of urinary bladder carcinogenicity in mice

Phosphorylated histone H2AX (γ‐H2AX) has been demonstrated as a DNA damage marker both in vitro and in vivo. We previously reported the effects of genotoxic carcinogens in the urinary bladder of rats by immunohistochemical analysis of γ‐H2AX using samples from 28‐day repeated‐dose tests. To evaluate the application of γ‐H2AX as a biomarker of carcinogenicity in the bladder, we examined species differences in γ‐H2AX formation in the urinary bladder of mice. Six‐week‐old male B6C3F₁ mice were treated orally with 12 chemicals for 4 weeks. Immunohistochemical analysis demonstrated that N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine, p‐cresidine and 2‐acetylaminofluorene (2‐AAF), classified as genotoxic bladder carcinogens, induced significant increases in γ‐H2AX levels in the bladder urothelium. In contrast, genotoxic (2‐nitroanisole, glycidol, N‐nitrosodiethylamine and acrylamide) and non‐genotoxic (dimethylarsinic acid and melamine) non‐bladder carcinogens did not upregulate γ‐H2AX. Importantly, 2‐nitroanisole, a potent genotoxic bladder carcinogen in rats, significantly increased the proportion of γ‐H2AX‐positive cells in rats only, reflecting differences in carcinogenicity in the urinary bladder between rats and mice. Significant upregulation of γ‐H2AX was also induced by uracil, a non‐genotoxic bladder carcinogen that may be associated with cell proliferation, as demonstrated by increased Ki67 expression. 2‐AAF caused γ‐H2AX formation mainly in the superficial layer, together with reduced and disorganized expression of uroplakin III, unlike in rats, suggesting the mouse‐specific cytotoxicity of 2‐AAF in umbrella cells. These results suggest γ‐H2AX is a useful biomarker reflecting species differences in carcinogenicity in the urinary bladder.     

Time dependence of chloroform-induced metabolic alterations in the liver and kidney of B6C3F1 mice

The time course of some biochemical changes in the liver and in the kidney was studied in B6C3F1 male mice dosed with a single i.p. injection of 150 mg/kg body weight (b.w.) CHCl₃. Hepatic and renal microsomal cytochrome P450 (P450) content and some related monooxygenase activities, CHCl₃ oxidative and reductive metabolism, cytosolic reduced glutathione (GSH) content and serum markers of nephrotoxicity were measured. In the liver no biochemical changes were produced up to a week after chloroform treatment. On the contrary, the drug-metabolizing enzyme system in the kidney was dramatically and rapidly inactivated by chloroform treatment. Maximum loss of GSH (50%), P450 (80%) and of different enzymatic activities, including CHCl₃ bioactivation, occurred during the first 5 h. These biochemical alterations are early effects, not secondary to morphological tissue changes. Kidney parameters, altered by chloroform treatment, returned to control values at different times: renal function markers became normal in 48 h; GSH levels were recovered at 96 h and the drug-metabolizing enzyme activities at longer times. The present results clearly show that repeated daily doses of chloroform, as those used in carcinogenicity tests, find renal tubular cells not at their physiological status, due to the changes produced by the first chloroform dose. Therefore the similarity in P450-dependent chloroform metabolism shown in vitro by hepatic and renal microsomes from untreated B6C3F1 male mice or in vivo in animals treated once, is lost during repeated treatments. These features should be considered in understanding the different susceptibility of the liver and the kidney to chloroform-induced tumours. Received: 18 May 1999 / Accepted: 19 July 1999     

Effects of 4-nonylphenol on adipogenesis in 3T3-L1 preadipocytes and C3H/10T1/2 mesenchymal stem cells

Obesogens are a subset of endocrine disruptor chemicals (EDCs) that cause obesity. The typical EDC 4-nonylphenol (4-NP) has been identified as an obesogen. However, the in vitro effects of 4-NP on adipogenesis remain unclear. In this study, 3T3-L1 preadipocytes and C3H/10T1/2 mesenchymal stem cells (MSCs) were used to investigate the influence of 4-NP on adipogenesis. The differentiation protocols for 3T3-L1 preadipocytes and C3H/10T1/2 MSCs took 8 and 12 days, respectively, beginning at Day 0. In differentiated 3T3-L1 preadipocytes, 20 μM 4-NP decreased cell viability on Days 4 and 8. Exposure to 4-NP inhibited triglyceride (TG) accumulation and adipogenic marker expression on Days 0–8, but the inhibitory effects were weaker on Days 2–8. The protein expression of pSTAT3 or STAT3 decreased on Days 0–8 and 2–8. Conversely, 4-NP promoted TG accumulation and the adipogenic marker expression in C3H/10T1/2 adipocytes. The opposing effects were attributed to physiological differences between the two cell lines. The 3T3-L1 preadipocytes are dependent on mitotic clonal expansion (MCE) to drive differentiation, while C3H/10T1/2MSCs and human preadipocytes are not. Additionally, 4-NP downregulated β-catenin expression in C3H/10T1/2 adipocytes. Accordingly, we hypothesized that 4-NP promotes adipogenesis. The role of the canonical Wnt pathway in the promotion of adipogenesis by 4-NP requires further validation. This study provides new insights into the mechanisms and appropriate risk management of 4-NP.     

Correlation between Bcl-2 overexpression and H-ras mutation in naturally occurring hepatocellular proliferative lesions of the B6C3F1 mouse.

The correlation between the mutation at codon 61 of the H-ras gene and the expression of the Bcl-2 protein was investigated in naturally occurring hepatocellular proliferative lesions in B6C3F1 mice. Specimens of histologically diagnosed neoplastic or preneoplastic lesions of the liver, obtained from the control mice used for 2-year carcinogenicity studies, were examined by immunohistochemical techniques. All of 25 lesions confirmed to be hepatocellular carcinomas stained positive for the Bcl-2 protein. Three of 12 foci of cellular alterations, as well as 24 of 42 hepatocellular adenomas, stained weakly positive. Bcl-2 protein was expressed to a greater degree in hepatocellular carcinomas as opposed to adenomas and confirmed by Western blot analysis. Seven of 18 hepatocellular adenomas that stained positive for Bcl-2 and three of 16 hepatocellular adenomas that stained negative had a mutation at codon 61 of the H-ras gene. Overexpression of Bcl-2 protein is likely to enhance the malignant turnover of the neoplastic cells, following a mutation at codon 61 of the H-ras gene particularly. These findings suggest that Bcl-2 overexpression and the mutation at codon 61 of the H-ras gene may be critical factors in the development of naturally occurring hepatocellular tumors in B6C3F1 mice.     

The effect of study type on body weight and tumor incidence in B6C3F1 mice fed the NTP-2000 diet

The B6C3F1 mouse is the standard mouse strain used in National Toxicology Program (NTP) carcinogenesis studies. Over time, increased liver tumorigenesis that was correlated with elevated body weights was noted in males and females. NTP therefore replaced the NIH-07 diet with the NTP-2000 diet and returned to group housing of females as lower body weights were noted in group housed mice. However, recent studies reported study-type differences in body weights at 3 months using the NTP-2000 diet with higher weights evident in drinking water and inhalation studies compared to feed studies. Therefore, body weight and tumor incidence data were collected for untreated control mice from all 2-year NTP feed (12), drinking water (8), water gavage (6) and inhalation (10) studies that used the NTP-2000 diet in order to assess the impact of study type on body weights and tumor incidences. Results show statistically significant elevated body weights and liver tumor incidences in males and females from drinking water, water gavage and inhalation studies compared to results from feed studies. Thus, the elevated body weights and liver tumorigenesis noted in mice using the NIH-07 diet were also evident using the NTP-2000 diet, which was introduced to address body weight elevations. Given the study-type dependent effects noted, these results emphasize the importance of carefully selecting historical control data for B6C3F1 mice. Moreover, because of the association between body weight and liver tumorigenesis, these results may have implications regarding dose-level selection for carcinogenicity studies involving B6C3F1 mice based on the maximum tolerated dose.     

Acrylonitrile is a multisite carcinogen in male and female B6C3F1 mice.

Acrylonitrile is a heavily produced unsaturated nitrile, which is used in the production of synthetic fibers, plastics, resins, and rubber. Acrylonitrile is a multisite carcinogen in rats after exposure via gavage, drinking water, or inhalation. No carcinogenicity studies of acrylonitrile in a second animal species were available. The current studies were designed to assess the carcinogenicity of acrylonitrile in B6C3F1 mice of both sexes. Acrylonitrile was administered by gavage at 0, 2.5, 10, or 20 mg/kg/day, 5 days per week, for 2 years. Urinary thiocyanate and N-acetyl-S-(2-cyanoethyl)-L-cysteine were measured as markers of exposure to acrylonitrile. In general, there were dose-related increases in urinary thiocyanate and N-acetyl-S-(2-cyanoethyl)-L-cysteine concentrations in all dosed groups of mice and at all time points. Survival was significantly (p < 0.001) reduced in the top dose (20 mg/kg) group of male and female mice relative to controls. The incidence of forestomach papillomas and carcinomas was increased in mice of both sexes in association with an increase in forestomach epithelial hyperplasia. The incidence of Harderian gland adenomas and carcinomas was also markedly increased in the acrylonitrile-dosed groups. In female mice, the incidence of benign or malignant granulosa cell tumors (combined) in the ovary in the 10 mg/kg dose group was greater than that in the vehicle control group, but because of a lack of dose response, this was considered an equivocal finding. In addition, the incidences of atrophy and cysts in the ovary of the 10 and 20 mg/kg dose groups were significantly increased. The incidences of alveolar/bronchiolar adenoma or carcinoma (combined) were significantly increased in female mice treated with acrylonitrile at 10 mg/kg/day for 2 years. This was also considered an equivocal result. In conclusion, these studies demonstrated that acrylonitrile causes multiple carcinogenic effects after gavage administration to male and female B6C3F1 mice for 2 years.     

Studies on the binding of [3H]flumazenil and [3H]sarmazenil in post-mortem human brain

Two benzodiazepine analogues, [³H]flumazenil and [³H]sarmazenil, were used to study the GABA_A/benzodiazepine receptor complex in human post-mortem brain using in vitro receptor assays on homogenates and whole hemisphere autoradiography. Both radioligands bound in a saturable manner to single binding sites in the tissue preparations from any brain region. The highest levels of binding were found in the cortical regions and in cortex cerebelli. Both [³H]flumazenil and [³H]sarmazenil were excellent radioligands for autoradiography with high binding in cerebral and cerebellar cortex with no or very low binding in areas with white matter. The addition of a high concentration of flumazenil or clonazepam did not inhibit the binding of [³H]sarmazenil to granule cells in the cerebellum while the binding of [³H]flumazenil was abolished completely in all regions. The results show that with the two different radioligands, one an antagonist and one a partial inverse agonist, the binding pattern to GABA_A/benzodiazepine receptor complex is approximately similar in most brain regions. The additional binding seen in the cerebellum with [³H]sarmazenil is suggested to be due to binding to an α₆-containing complex.     

基于RBL-2H3细胞和ICR小鼠过敏与类过敏叠加模型评价注射用血塞通(冻干)过敏与类过敏反应

目的 建立过敏和类过敏叠加的RBL-2H3细胞和ICR小鼠动物模型,对注射用血塞通(冻干)(XST)的过敏与类过敏反应进行评价研究。方法 体外以RBL-2H3细胞的β-氨基己糖苷酶(β-Hex)和组胺释放率为评价指标,确定抗二硝基苯单克隆抗体(DNP-IgE)、DNP-牛血清白蛋白(BSA)的剂量及与C48/80(30 μg·mL^-1)作用的最佳时间,筛选过敏和类过敏叠加模型的阳性条件,随后考察XST (4、8、16 mg·mL^-1)对细胞活力及与DNP-IgE/BSA叠加后对细胞脱颗粒的影响。体内以ICR小鼠为实验对象,以(类)过敏反应症状分值及血浆中免疫球蛋白E (IgE)、组胺、5-羟色胺、血管内皮生长因子A (VEGF-A)、末端补体复合物(SC5b-9)含量为评价指标,筛选卵蛋白(OVA,2.5、5.0、10.0 mg·kg^-1)、C48/80(1、2、4 mg·kg^-1)过敏-类过敏模型阳性条件,最后对XST (60、120、240 mg·kg^-1)的致敏性及是否会产生过敏、类过敏反应进行评价。结果 体外细胞实验最终确定400 ng·mL^-1的DNP-IgE致敏后用50 ng·mL^-1的DNP-BSA激发的同时与C48/80共同作用30 min作为过敏与类过敏叠加阳性组;16 mg·mL^-1的XST与DNP-IgE/BSA联合叠加时,与单给DNP-IgE/BSA或XST组比较均促进组胺和β-Hex的释放(P<0.01)。体内小鼠实验中5、10 mg·kg^-1的OVA均会使小鼠体内IgE显著升高,依据过敏样反应分值和小鼠血浆内组胺、VEGF-A和SC5b-9含量最终确定5 mg·kg^-1 OVA与1 mg·kg^-1 C48/80建立叠加模型,耳、肺及支气管组织中可见明显的水肿及炎性细胞浸润。单纯的XST不会对小鼠致敏,但是与OVA介导的过敏反应叠加后,与单给DNP-IgE/BSA或XST组比较,会显著提高血浆中内组胺、VEGF-A和SC5b-9水平(P<0.05、0.01),与建立的过敏-类过敏叠加模型表现出较好地一致性。结论 体外体内实验均表明IgE介导的过敏反应和C48/80引起的类过敏反应会产生叠加作用,加剧过敏介质的释放和免疫反应程度。同时此模型的建立也验证了XST存在过敏与类过敏叠加现象,该模型可为中药注射剂的临床前安全性评价及合理用药提供参考。     

4-tert-octylphenol regulates the differentiation of C3H10T1/2 cells into osteoblast and adipocyte lineages.

The aim of this study was to investigate whether 4-tert-octylphenol (OP) affects the differentiation of multipotent C3H10T1/2 cells, a cell line established from mouse embryonic connective tissue, into osteoblast and adipocyte lineages. Confluent C3H10T1/2 cells were incubated for 7 days with (OP-treated cultures) or without (control cultures) 15 microg/ml of OP. The 7-day treatment of confluent cells with OP decreased alkaline phosphatase activity by 81%, inhibited the expression of transforming growth factor beta2, and inhibited the morphological changes in cells to an osteoblastic appearance. These results indicate that the 7-day treatment of confluent C3H10T1/2 cells with OP inhibited their differentiation into osteoblasts. Since this treatment strongly induced the expression of peroxisome proliferator-activated receptor r (PPARr) but did not stimulate triacylglycerol (TG) accumulation in cells, C3H10T1/2 cells in the control and OP-treated cultures were incubated for 2 days with a hormone mixture (insulin [INS], dexamethasone, and 1-methyl-3-isobutylxanthine) and incubated for an additional 5 days with INS alone. The TG and adiponectin contents of the OP-treated cultures were 4.2 and 4.1 times higher, respectively, than those of the control cultures. There were many more Oil Red O-staining cells in the OP-treated cultures than in the control cultures. The expression of PPARr in the OP-treated cultures was higher than that in the control cultures. These results indicate that the OP-treated cultures contained a larger number of adipocytes than the control cultures. In conclusion, treatment of C3H10T1/2 cells with OP inhibited osteoblast differentiation, causing a lineage shift toward adipocytes.