Delayed DNA synthesis induced by 3-aminobenzamide in partially hepatectomized liver of rats.

The possibility of poly(ADP-ribosyl)ation playing a role during liver regeneration induced by partial hepatectomy (PH) in vivo was examined. When rats were given an i.p. injection of 3-aminobenzamide (ABA) at a dose of 600 mg/kg body weight 12 h after PH, the levels of DNA synthesis at 20 h after PH were significantly reduced. The time course of DNA synthesis in regenerating liver was significantly delayed in the ABA-treated group. Enzymatic assay revealed the activity of poly-(ADP-ribose)polymerase (PADPRP) in controls to be increased in parallel with the increase of DNA synthesis induced by PH. This increase in PADPRP activity was delayed and very much weaker after ABA treatment. The results thus suggested that poly(ADP-ribosyl)ation might play an important role in DNA synthesis during liver regeneration in vivo.     

Enhanced incorporation of thymidine into DNA in the liver of intact and partially hepatectomized rats pretreated with 5-azacytidine.

The administration of 5-azacytidine to rats resulted in enhancement of thymidine incorporation into liver DNA. Repeated doses of the drug caused a greater than 10-fold increase of thymidine incorporation. In 5-azacytidine-treated intact rats no changes in the activity of thymidine and thymidylate kinases were observed, whereas a marked depression of thymidine phosphorylase activity occurred. In intact animals the mitotic activity in the drug-treated livers changed slightly; however, 5-azacytidine administration before partial hepatectomy resulted in a dramatic increase of mitotic activity in 24-hr regenerating livers. In this case the observed increase in incorporation of thymidine was paralleled both by increased activity of thymidine and thymidylate kinases and by a decline in thymidine phosphorylase activity. The higher incorporation of radioactivity into liver DNA in intact rats pretreated with the drug can be accounted for, at least partially, by the lower cellular degradation of the injected radioactive thymidine used for labeling. In addition, alterations in the labeling and in the mitotic activity of hepatocytes and nonparenchymal cells caused by 5-azacytidine should be taken into consideration.     

Selective resistance to cytotoxic agents in hepatocytes isolated from partially hepatectomized and neoplastic mouse liver

Hepatocytes were isolated from B6C3F1 male mouse neoplastic livers (containing hepatocellular adenomas and carcinomas) or two-thirds partially hepatectomized livers and tested in primary culture for their cytotoxic response to hepatotoxins. Partially hepatectomized mouse hepatocytes were less sensitive to lindane, methotrexate, diethylnitrosamine and adriamycin, and more sensitive to cycloheximide compared to normal mouse hepatocytes. Neoplastic hepatocytes were less sensitive to lindane and methotrexate, did not differ in cytotoxic response to diethylnitrosamine and adriamycin and were more sensitive to cycloheximide compared to normal mouse hepatocytes.     

Hepatic cyst formation in male rats partially hepatectomized as weanlings during short-term feeding of 2-acetylaminofluorene

Partial hepatectomy (p.h.) of weanling male Sprague-Dawley ratsduring short-term feeding of 0.03% 2acetylaminofluorene (AAF)resulted, 12 to 15 months later, in a massive production ofhepatic cysts. The weight of the right lateral and caudate lobesplus neoplasms (the left lateral and median lobes were excisedat the time of p.h.) accounted for as much as 43% of total bodyweight. The incidence of hepatic cysts was negligible when animalswere not subjected to p.h. during AAF feeding. The feeding of0.05% phenobarbital (PB) subsequent to AAF + p.h. did not significantlyincrease the incidence of hepatic cysts. By comparison of thepresent data with that of other investigators, it can be suggestedthat susceptibility to cholangioma formation following AAF +p.h. may be determined in part by the developmental stage ofthe rat and/or its liver at the time of the AAF + p.h. regimen.     

慢性间歇性低压低氧预处理可减轻大鼠放射性心脏损伤

目的 研究慢性间歇性低压低氧(CIHH)对急性期放射性心脏损伤影响及作用机制。方法 成年雄性SD大鼠48只随机分为空白对照组、CIHH组、照射组和CIHH+照射组。CIHH处理为动物在接受照射前置于低压氧仓预处理。记录左心室功能,测定心肌梗死面积。Masson染色后计算心肌胶原容积分数(CVF),ELISA法检测心肌组织总超氧化物歧化酶(T-SOD)活力和丙二醛(MDA)含量。蛋白印迹法检测纤维化标志物Ⅰ型胶原(COL-1)、内质网应激相关蛋白GRP78和CHOP表达情况。差异检验采用双因素方差分析。结果 CIHH预处理后再照射大鼠左心室收缩及舒张功能有所改善,心肌梗死面积减小。CIHH+照射组较照射组CVF下降同时伴随COL-1表达水平降低(P<0.01,P<0.01)。CIHH+照射组T-SOD活力较照射组明显升高[(185.19±3.20) U/mgprot∶(156.61±4.60) U/mgprot,P<0.01],MDA浓度下降[(1.36±0.17) nmol/mgprot∶(2.36±0.21) nmol/mgprot,P<0.01]。CIHH+照射组与照射组比较内质网应激标志性蛋白GRP78和CHOP蛋白水平亦均降低(P<0.05,P<0.01)。结论 CIHH预处理在一定程度上能改善放射线引起的冠状动脉损伤,增强心脏对缺血再灌注损伤耐受性,减小缺血再灌注后心肌梗死面积,并减少小血管周围和心肌间质胶原沉积。CIHH可能通过抑制氧化应激、内质网应激及抑制心肌纤维化等对心肌起保护作用。     

Enhancement of radiation-induced normal tissue damage by a fibrosarcoma

Normal tissue damage in the legs of mice was enhanced by the presence of a fibrosarcoma (FSa I) in the leg at the time of treatment with single doses of 30 to 70 Gy. Damage was assessed by measuring leg contracture 23 to 365 days after irradiation of 8 mm diameter tumors. Animals with and without tumors were treated with 1.0 mg misonidazole/g body weight 30 min before irradiation to ensure that the tumors did not recur and interfere with the assessment of contracture. The data suggest that in some cases, late damage may be enhanced by destructive effects of the tumor on the tumor bed.     

Amelioration of doxorubicin-induced cardiac and renal toxicity by pirfenidone in rats

Purpose Doxorubicin (DXR) is an anthracycline glycoside with a broad spectrum of therapeutic activity against various tumors. However, the clinical use of DXR has been limited by its undesirable systemic toxicity, especially in the heart and kidney. This study was designed to test the effectiveness of dietary intake of pirfenidone (PD) against DXR-induced cardiac and renal toxicity.Methods Male Sprague Dawley rats were placed into four treatment groups: saline injected intraperitoneally (i.p.) plus regular diet (SA+RD); DXR i.p. plus regular diet (DXR+RD); saline i.p. plus the same diet mixed with 0.6% PD (SA+PD); and DXR i.p. plus the same diet mixed with 0.6% PD (DXR+PD). The animals were fed regular or regular plus PD diets 3 days prior to i.p. injections of either saline or DXR and continuing throughout the study. A total dose of DXR (16.25 mg/kg) or an equivalent volume of saline was administered in seven injections (2.32 mg/kg per injection) three times per week with an additional dose on the 12th day. At 25 days following the last DXR or saline injection, some animals were anesthetized for the measurement of cardiac and pulmonary function, and others were killed by an overdose of pentobarbital. At the time the animals were killed, abdominal fluid was collected. Kidney and heart were removed, weighed, fixed with 10% formalin or frozen in liquid nitrogen. The fixed tissues were used for histological examination and the frozen tissues were used for biochemical studies.Results The average volumes of abdominal fluid in the DXR+RD and DXR+PD groups were 9.42 ml and 3.42 ml and the protein contents of abdominal fluid in the DXR+RD and DXR+PD groups were 218 mg and 70 mg, respectively. A 12.5% mortality occurred in the DXR+RD group as compared to 0% in DXR+PD group. There were no changes in any of the cardiac or pulmonary physiological parameters in any of the four groups. The changes in the heart and kidney of the DXR+RD group included reduction in organ weight, increase in hydroxyproline content of heart, increase in hydroxyproline, and lipid peroxidation in the kidney and plasma, and increase in protein concentration in urine as compared to rats in the control, SA+RD and SA+PD groups. Treatment with PD abrogated the DXR-induced increases in hydroxyproline content in the heart and kidney, lipid peroxidation of the kidney and plasma, and protein content of the urine in the DXR+PD group. DXR treatment alone caused disorganization of cardiac myofibrils, vacuolization of the myofibers, and renal tubular dilation with protein casts in both the cortical and medullary regions. Treatment with PD minimized the DXR-induced histopathological changes of heart and kidney in the DXR+PD group.Conclusions Treatment with PD reduced the severity of DXR-induced toxicity as assessed by reduced mortality, diminished volume of recovered fluid in the abdominal cavity, and severity of cardiac and renal lesions at both the biochemical and morphological levels. These results indicate that PD has the potential to prevent DXR-induced cardiac and renal damage in humans on DXR therapy.     

Molecular assays of radiation-induced DNA damage

There is a need for assays of DNA damage in many areas of laboratory research applied to radiation therapy, in order to understand the molecular processes involved in cell killing by ionising radiation and to predict in vivo response. Assays exist which measure many types of DNA damage following ionising radiation. From studies of the dose-response relationships for different types of damage, the double-strand break (dsb) has been shown to be the most significant lesion. Assays for DNA dsb have been of low sensitivity, such that supralethal doses of radiation had to be used in order to study dsb induction or repair. New assays, such as pulsed-field gel electrophoresis, are sensitive to dsb in a dose range relevant to cell survival. In addition, these assays can assess the distribution of dsb in different parts of the genome and determine heterogeneity of damage induction and repair. Assays which measure the effects of strand breaks on DNA complexed with nuclear matrix can reveal features of chromatin organisation and their influence on cellular radiosensitivity.