A processive versus a distributive mechanism of action correlates with differences in ability of normal and xeroderma pigmentosum group A endonucleases to incise damaged nucleosomal DNA

A DNA endonuclease, isolated from the nuclei of normal human and xeroderma pigmentosum complementation group A (XPA) cells, which recognizes predominately pyrimidine dimers, was examined for the mechanism by which it locates sites of damage on UVC-irradiated DNA. In reaction mixtures with low ionic strengths (i.e. lacking KCl), the normal and XPA endonuclease locate sites of UV damage on both naked and reconstituted nucleosomal DNA by different mechanisms. On both of these substrates, the normal endonuclease acts by a processive mechanism, meaning that it binds non-specifically to DNA and scans the DNA for sites of damage, whereas the XPA endonuclease acts by a distributive one, meaning that it randomly locates sites of damage on DNA. However, while both the normal and XPA endonucleases can incise UVC irradiated naked DNA, they differ in ability to incise damaged nucleosomal DNA. The normal endonuclease showed increased activity on UVC treated nucleosomal DNA compared with naked DNA, whereas the XPA endonuclease showed decreased activity on the damaged nucleosomal substrate. Since a processive mechanism of action is sensitive to the ionic strength of the micro-environment, the KCl concentration of the reaction was increased. At 70 mM KCI, the normal endonuclease switched to a distributive mechanism of action and its ability to incise damaged nucleosomal DNA also decreased. These studies show that there is a correlation between the ability of these endonucleases to act by a processive mechanism and their ability to incise damaged nucleosomal DNA; the normal endonuclease, which acts processively, can incise damaged nucleosomal DNA, whereas the XPA endonuclease, which acts distributively, is defective in ability to incise this substrate.      

A new amino acid mixture permits new approaches to the treatment of phenylketonuria

A new amino acid mixture for incorporation into medical foods for the treatment of hyperphenylalaninemia has been tested in a regular clinic. The mix is designed to be as unobtrusive as possible, consistent with good nutrition. After more than 1 year of trial as a beverage, we have shown that it is safe and well tolerated but that plasma phenylalanine is no better controlled than with some other products. The mix can be incorporated into a large number of different foods without affecting the taste. Occult monitoring of the quantity of medical foods purchased compared with the amounts reported to be consumed in diet histories provides an excellent way to monitor dietary compliance.     

B7-1和IL-12基因转染对肝癌细胞免疫原性的影响

目的 观察Ｂ７－１和ＩＬ－１２基因表达对人肝癌细胞免疫原性原影响。方法 分别将Ｂ７－１和ＩＬ－１２基因以逆转录病毒介导转染ＨｅｐＧ２细胞。阳性克隆细胞与健康人外周血淋巴细胞（ＰＢＬ）混合培养后,用流式细胞仪检测ＰＢＬ表面Ⅰ类人白细胞抗原（ＨＬＡ－Ⅰ）分子表达,以ＭＴＴ法检测ＰＢＬ的特异性杀伤活性Ｋ５６２细胞的活性。结果 混合ＨｅｐＧ２／Ｂ７－１ＨｅｐＧ２／ＩＬ－１２细胞组ＰＢＬ表面的ＨＬＡ－Ⅰ分子     

国内六大行政区域六城市中老年人群膝关节骨性关节炎患病危险因素比较

目的：了解中国不同地区间中老年人群膝关节骨性关节炎患病危险因素。方法：调查时间为2005—07／08。①从中国六大行政区（西北，华北，华东。中南，东北，西南）选出六城市（西安，石家庄，上海。广州，哈尔滨市，成都），用分层多阶段整群抽样方法，抽取6218名40岁及以上具有正式户口常住男女人群进行膝关节骨性关节炎的流行病学问卷调查（包括一般情况、现病史、既往史、体格检查、X射线片检查情况和疾病诊断6个方面，共计94个问题141个变量指标），并对其中4808名有症状者进行X射线平片膝正侧位投照。②膝关节骨性关节炎诊断标准为临床症状阳性加X射线Kellgren ＆ Lawrence分级二级及以上者。③计算患病率，并采用Epilnf06．0和SPSS 10．0软件对其中83个变量进行多因素非条件Logistfc回归分析，表示疾病与暴露因素之间联系强度的指标用比值比（OR），若OR〉1，说明疾病发生危险性增加，与暴露因素呈正关联；若OR〈1，说明疾病发生危险性减少，与暴露因素呈负关联。 结果：①六城市膝关节骨性关节炎总患病率为15．6％，其中西安7．7％，石家庄11．2％，上海9．8％。广州30．5％，哈尔滨16．9％，成都17．5％，各城市患病率比较差异显著（P〈0．01）。②Logistic回归分析膝关节骨性关节炎在大部分城市有共同的危险因素如年龄大（OR=1．032—1．181），使用蹲坑排便年限长（OR=1．021-1．077），体质量高（OR=1．048—1．073），和开始饮酒年龄大（OR=1．008～1．028）；而从事专职体育运动（OR=1．651，西安），骨质疏松病史（OR=3．311，石家庄），吸烟（OR=2．654，石家庄），类风湿关节炎病史（OR=4．964，上海），文化程度高（OR=2．593，上海），女性（OR=2．510，广州），姐妹骨关节炎史（OR=13．251，哈尔滨），母亲骨关节炎史（OR=5．683，成都）等危险因素分别在不同地区出现． 结论：年龄大、使用蹲坑排便年限长、体质量高和开始饮酒年龄大是中国六地区膝关节骨性关节炎患病的共同危险因素，同时，不同地区主要危险因素又有一定差异。     

Mammographic findings after breast cancer treatment with local excision and definitive irradiation

Following local excision and definitive irradiation of 163 breast cancers in 160 women, alterations in mammographic patterns were observed for up to 7 years. Skin thickening was observed in 96% of mammograms obtained within 1 year of completing therapy and was most pronounced in women treated with iridium implant, chemotherapy, or axillary dissection. In 76% of mammograms, alterations in the parenchymal pattern, including coarsening of stroma and increased breast density, were seen at 1 year. Neither skin nor parenchymal changes progressed after 1 year. Within 3 years of treatment the parenchymal density, which usually regressed, did not change in all patients. At 3 years skin thickness and the parenchymal pattern had returned to normal in less than 50% of the breasts of these women. Scars developed in approximately one-quarter of women. They were present on the initial post-treatment mammogram and remained unchanged on serial studies. Coarse, benign calcifications also developed in the breasts of about one-quarter of women. Microcalcifications developed in 11 breasts; biopsy specimens of six were benign. Benign microcalcifications may be related to therapy.     

Lymphangiomas in children: MR imaging

Seventeen lymphangiomas in 15 patients were imaged with magnetic resonance (MR) to define the nature, extent, and anatomic relationships of these lesions. The MR and pathologic findings were then compared to determine the histologic basis for the signal-intensity characteristics of these lesions. The signal intensity of 13 lesions was similar to or slightly less than that of muscle on T1-weighted images and greater than that of fat on T2-weighted images. This appearance correlated with the presence of ectatic lymphatic channels containing clear fluid on histologic section. Four lymphangiomas had high signal intensity, approximately equal to that of fat, on T1-weighted images, reflecting the presence of clotted blood or small cystic spaces with a higher ratio of fat to fluid. Sixteen of 17 lesions had visible septations on MR images. The authors' experience suggests that most lymphangiomas have a characteristic appearance on MR images. The information obtained with MR imaging can help in providing a preoperative diagnosis, in planning surgical resection, and in defining recurrence.     

Liver metastases: detection by phase-contrast MR imaging

Forty patients with biopsy-proved metastatic liver cancers were studied by magnetic resonance (MR) imaging using one or more conventional (in-phase) pulse sequences and a corresponding phase-contrast (opposed-phase) pulse sequence. Pulse-sequence performance was quantitated by measuring signal-difference-to-noise (SD/N) ratios between cancerous tissue and liver. The SD/N performance of T2-weighted spin-echo (SE) pulse sequences improved when used with the phase-contrast technique. SE 2,000/30 opposed-phase images showed improved (P less than .001) SD/N in 72% of patients over in-phase images. The SD/N of T1-weighted SE or inversion recovery pulse sequences deteriorated when used with the phase-contrast technique. Changes in measured SD/N correlated well with image appearance and actual lesion detectability in individual cases. Phase-contrast imaging should be employed routinely when T2-weighted SE pulse sequences are relied on to detect liver cancer.