Benzamide potentiation of the cytotoxicity of bifunctional galacticol in resistant P388 leukemia correlates with inhibition of DNA ligase II

Summary Benzamide (BA) enhances the cytotoxicity of 1,2:5,6-dianhydrogalactitol (DAG) in resistant P388 leukemia cell lines but not in the sensitive parent line. To examine the reason for this difference in response, we carried out an alkaline elution assay using proteinase K to study DNA interstrand cross-linking. At early time points, equal concentrations of DAG produced the same level of interstrand cross-linking (ICL) in the resistant and sensitive P388 leukemic cells, although marked differences were observed in their cytotoxicity toward the two cell lines. In the sensitive cells, neither the amount of DNA cross-linking nor the cytotoxicity changed during the observation period (38 h) in either the presence or the absence of BA. In contrast, the elution rate of the DNA of DAG-treated resistant cells increased with time and had reached the control levels by 38 h. However, when these cells were postincubated with BA for 38 h, the elution rate of DNA was much faster than that observed for the untreated resistant cells, indicating an accumulation of DNA singlestrand breaks (SSB). The SSB accumulation caused by BA was associated with an inhibition of the activity of ligase II enzyme, which was stimulated when resistant cells were treated with DAG alone. The potentiating effect of BA on the resistant cells can thus be related to the inhibiting action of BA on the DNA-rejoining enzyme, ligase II. The lack of sensitization by BA of the DAG-treated parent cell line may be attributable to the absence of DNA-SSB formation, which is necessary for ligase II activation through the stimulation of poly(ADP-ribose) synthesis.     

Identification of widespread Helicobacter hepaticus infection in feces in commercial mouse colonies by culture and PCR assay.

The identification of a new murine pathogen, Helicobacter hepaticus, and its association with chronic active hepatitis and liver tumors prompted an evaluation of the prevalence of H. hepaticus in commercially available mice. Of the 28 different strains or stocks, totaling 160 mice from four major commercial vendors, cultured for H. hepaticus, 100% of mice from two outbred strains from one vendor were infected with H. hepaticus, whereas 9 of 13 inbred mouse strains from another vendor were infected. This high prevalence of H. hepaticus established a need for a rapid and reproducible, noninvasive assay for the screening of colony-maintained mice being used for biomedical research. The culturing of fecal material by using 0.45-microns-pore- size filtration for H. hepaticus consistently yielded reproducible results but required extended periods of time. (1 to 3 weeks) to obtain a definitive answer. Although it is rapid, the use of a direct PCR-based detection assay with fecal specimens is restricted by inhibitory agents. to circumvent these inhibitory agents and to augment our H. hepaticus culture technique, we have developed a novel PCR system in which the bacteria are isolated from fecal material in the presence of polyvinylpyropyrollidone and lysed by treatment with Chelex 100. The PCR is performed with Tth polymerase supplemented with a polymerase enhancer. By this PCR method, 24 H. hepaticus culture-positive and 30 H. hepaticus culture-negative fecal samples were correctly identified. Moreover, two samples which were PCR positive and culture negative initially were positive by both methods upon retesting of fresh material. Southern blot hybridizations and sequencing of PCR products showed them to be H. hepaticus specific. A comparison of results obtained under identical conditions indicated a 100-fold increase in sensitivity with Tth polymerase over Taq polymerase. This PCR method can be used as a noninvasive means of rapidly screening large numbers of colony mice for H. hepaticus.     

Empowering research: statistical power in general practice research

BACKGROUND: Statistical power is a measure of the extent to which a study is capable of discerning differences or associations which exist within the population under investigation, and is of critical importance whenever a hypothesis is tested by statistics. Conventionally, studies should reach a power level of 0.8, such that four times out of five a false null hypothesis will be rejected by a study. Statistical power may most easily be increased by increasing sample size. OBJECTIVE: We aimed to assess the level of statistical power of general practice research. METHODS: A total of 1422 statistical tests in 85 quantitative original papers in the British Journal of General Practice were analysed for statistical power. RESULTS: The median power of tests analysed was 0.71, representing a slightly greater than two-thirds likelihood of rejecting false null hypotheses. Of 85 studies, 37 (44%) attained power of 0.8 or more. Ten studies had power of more than 0.99 suggesting 'over-powering'. Twenty- one of the papers surveyed (25%) had a likelihood of gaining significant results poorer than that obtained by tossing a coin when a null hypothesis is false. CONCLUSION: While achieving higher power than studies in similar surveys of other disciplines, the power of general practice research falls short of the 0.8 convention. Adequate power is essential so that effects which exist are not missed. Recommendations are made concerning power calculations prior to the start of research and reporting of results in journal articles.      

The temporal pattern of recovery of myocardial perfusion and metabolism delineated by positron emission tomography after coronary thrombolysis

Recovery of mechanical function by ischemic myocardium is dependent on the restoration of nutritive blood flow and oxidative metabolism subsequent to reperfusion. To characterize the time course and extent of recovery of perfusion and metabolism, we used positron emission tomography with 15O-labeled water and 11C-labeled palmitate to sequentially study six dogs after 2 hr of ischemia followed by reperfusion for 4 wk. Myocardial blood flow in the ischemic region increased from 15 +/- 8% of normal during coronary occlusion to 82 +/- 25% 1 hr after reperfusion. Despite maintained coronary patency documented angiographically, flow was reduced after 24 hr to 37 +/- 16% of normal. This decrease was temporary, with flow returning to 66 +/- 11%, 62 +/- 7%, and 64 +/- 18% of normal after 1, 2, and 4 wk of reperfusion, respectively. Uptake of 11C-labeled palmitate paralleled alterations in perfusion during ischemia and early reperfusion, averaging 32 +/- 15% of normal during ischemia, and 67 +/- 22% and 36 +/- 10% after 1 and 24 hr of reperfusion. After that, palmitate uptake was more variable. Flow and fatty acid uptake after 4 wk of reperfusion were not related to collateral flow during ischemia or the extent of initial reperfusion. However, uptake of palmitate 1 hr after reperfusion was a strong predictor of the uptake of palmitate 4 wk after reperfusion (r = 0.86, p less than 0.03). The results indicate that positron emission tomography with 15O-labeled water and 11C-labeled palmitate may be useful for assessing the success of recanalization in restoring nutritive perfusion and fatty acid metabolism and that the uptake of [11C]palmitate early after reperfusion predicts the ultimate salvage of myocardium.     

Brain dysfunction in social drinkers

Thirty-four social drinkers who had referred themselves to the Regional Brain Damage Unit for assessment of the effects of drinking alcohol were compared with 42 volunteer control subjects of equivalent age but with low alcohol intake, using two 'learning' tests — the Rey Auditory Verbal Learning Test (RAVLT) and the Austin Button Maze. The Maze Test gave no evidence of disorder, but the two groups were significantly different on the RAVLT. No abnormalities in standard cognitive tests were apparent. These results suggest that a deficit in learning ability may be an early feature of the brain dysfunction associated with excessive alcohol consumption.     

Interventional dysrhythmia management and the role of laser

Drug-resistant dysrhythmias may require interventional management. Laser energy can be used for interruption or destruction of dysrhythmia-generating foci or conductive pathways. Lasers may, therefore, be useful tools for interventional management of supraventricular or ventricular dysrhythmias and preexcitation syndromes. Although the role of lasers in interventional dysrhythmia management is not clearly defined, the advantages may be substantial.