Clueless forms dynamic, insulin-responsive bliss particles sensitive to stress.

Drosophila Clueless (Clu) is a ribonucleoprotein that directly affects mitochondrial function. Loss of clu causes mitochondrial damage, and Clu associates with proteins on the mitochondrial outer membrane. Clu's subcellular pattern is diffuse throughout the cytoplasm, but Clu also forms large mitochondria-associated particles. Clu particles are reminiscent of ribonucleoprotein particles such as stress granules and processing bodies. Ribonucleoprotein particles play critical roles in the cell by regulating mRNAs spatially and temporally. Here, we show that Clu particles are unique, highly dynamic and rapidly disperse in response to stress in contrast to processing bodies and autophagosomes. In addition, Clu particle formation is dependent on diet as ovaries from starved females no longer contain Clu particles, and insulin signaling is necessary and sufficient for Clu particle formation. Oxidative stress also disperses particles. Since Clu particles are only present under optimal conditions, we have termed them "bliss particles". We also demonstrate that many aspects of Clu function are conserved in the yeast homolog Clu1p. These observations identify Clu particles as stress-sensitive cytoplasmic particles whose absence corresponds with altered cell stress and mitochondrial localization.

Assessment of adenosine, arbutamine and dobutamine as pharmacological stress agents during (99m)Tc-tetrofosmin SPECT imaging: a randomized study.

We evaluated the use of adenosine, dobutamine and arbutamine with (99m)Tc-tetrofosmin myocardial perfusion imaging. Forty patients under investigation for suspected coronary artery disease were recruited. Each had a resting scan and two separate stress scans on different days, in a randomized cross-over study. Resultant images were blindly reported in 13 segments per scan as normal, reversible or fixed defects. A score was given (0-3) for segmental defect severity. Haemodynamic responses were as expected for each agent. Subjective side effect scores did not differ overall between agents. Adenosine caused a significantly higher incidence of abnormal taste (54%) than dobutamine and arbutamine (both 23%) and a lower incidence of palpitations (25% vs 69% and 54%, respectively), all P<0.05. Arbutamine caused significantly more chest pain than adenosine (77% vs 46%) though less flushing (35% vs 68%), both P<0.05. Comparison of the results obtained showed highly significant levels of segmental agreement for visual and semi-quantitative analysis between adenosine and arbutamine, kappa value and correlation coefficient of 0.78 and 0.86, respectively, dobutamine and adenosine 0.69 and 0.78, and arbutamine and dobutamine 0.75 and 0.78, all P<0.0001. Adenosine, arbutamine and dobutamine differ in their haemodynamic response and side effect profile but provide highly comparable results during (99m)Tc SPECT imaging.

The routine use of sublingual GTN with resting 99Tcm-tetrofosmin myocardial perfusion imaging.

Nitrates can be used to improve resting myocardial blood flow in patients with severe coronary artery disease. This may enhance tracer uptake during rest myocardial perfusion imaging. Recent studies using nitrates at rest have shown increased detection of reversible ischaemia in this patient group with the 201Tl and 99Tcm perfusion tracers MIBI and tetrofosmin. However, it is not always possible to assess the severity of coronary artery disease before the rest injection and therefore whether a patient would benefit from nitrate administration. To improve the sensitivity for the detection of reversible ischaemia and to avoid a repeat study with nitrates (especially in patients with 'fixed' defects), a protocol in which all patients routinely receive nitrates prior to the rest injection is required. This prospective study evaluated the effect of nitrate administration prior to rest imaging in a randomly selected group of patients. Thirty patients selected at random from routine referrals had stress, rest and rest + GTN tetrofosmin imaging on three separate days. Changes in reversibility between the rest and rest + GTN images were assessed both visually and using semi-quantitative analysis. Defects at stress were seen in 43 coronary artery territories, 33 of which were reversible at rest and 37 reversible at rest + GTN. Of these 43 defects, 82% demonstrated either increased or the same degree of reversibility at rest + GTN imaging compared to standard rest imaging. All defects with reduced reversibility at rest + GTN imaging (i.e. the remaining 18%) were, however, still reversible compared to the stress images. Some of this reduced reversibility may be due to attenuation artefacts. We conclude that the routine use of GTN with rest tetrofosmin imaging will result in increased detection of ischaemic areas with no loss of sensitivity or specificity.

The use of GTN to improve the detection of ischaemic myocardium using 99Tcm-tetrofosmin.

Recent work has shown that rest 99Tcm-sestamibi uptake may underestimate the amount of perfused myocardium, suggesting infarct tissue in some instances when myocardium is hypoperfused but which will benefit from revascularization. Administration of nitrates before a resting 99Tcm-sestamibi injection has been shown to increase tracer uptake. We have used 99Tcm-tetrofosmin as a myocardial perfusion agent and imaged 30 patients at stress, rest and again at rest following administration of sublingual nitrates. All patients had angiographically demonstrated severe coronary artery disease and 27 patients had previous infarction. Twenty-one patients were stressed on a treadmill and nine using intravenous dobutamine. Images were analysed using both a visual and semi-quantitative analysis. Defects were observed in 39 coronary artery territories on stress 99Tcm-tetrofosmin imaging, 23 appearing fixed on standard rest imaging. Twelve (52%) of these defects showed reversibility on rest with glyceryl trinitrate (GTN) imaging and increased reversibility was seen in 62% of defects reversible at rest. We conclude that, in patients with severe coronary artery disease and fixed rest defects, GTN given prior to the rest injection appears to improve the detection of ischaemic hypoperfused myocardium.

Evaluation of 99Tcm-tetrofosmin as a myocardial perfusion agent in routine clinical use.

Recent trials with selected patients have indicated that 99Tcm-tetrofosmin is a suitable agent for myocardial perfusion imaging. We performed 99Tcm-tetrofosmin perfusion imaging in an unselected group of 297 patients routinely referred to our department. Single photon emission tomographic (SPET) imaging was performed 45-60 min post-injection using a 2-day stress and rest protocol. Altogether, 192 patients were stressed on a treadmill and 105 using intravenous dobutamine. Comparison with angiography was possible in 86 patients, 65 of whom had atheromatous coronary artery disease and 21 of whom had normal coronary arteries (6 of whom fulfilled the criteria for syndrome X). The sensitivity for the detection of coronary artery disease was 94% (93% for exercise stress and 95% for dobutamine). The overall specificity was 85% (87% for exercise stress and 80% for dobutamine in the 15 normal patients and the segments supplied by disease-free coronary vessels in patients with disease elsewhere). We conclude that 99Tcm-tetrofosmin is a highly sensitive and specific agent for the detection of coronary artery disease, using both exercise and dobutamine stress, with few limitations.

Limb blood flow measurement in technically successful balloon angioplasty.

An isotope limb blood flow technique was used to assess the outcome of technically successful balloon angioplasty. Measurements were made on a total of 120 limbs, before angioplasty and at least once after angioplasty at 3 weeks, 3 months, 6 months, 12 months and 2-5 years. 67% of treated limbs showed a significant improvement in limb blood flow at 3 weeks. At 12 months following angioplasty 43% of limbs still showed an improvement in blood flow compared with the measurement made before angioplasty. However, a number of these limbs showed a significant fall in limb blood flow between 3 weeks and 12 months even though the 3 week and the 12 month flow figures were still greater than those before angioplasty. The degree of initial improvement in blood flow seen at 3 weeks persisted at 12 months after angioplasty without significant fall in only 30% of limbs. In 33% of limbs where the balloon angioplasty was technically successful there was no improvement in blood flow at 3 weeks. 80% of these limbs had further significant untreated disease angiographically, compared with 43% of limbs where there was an increase in limb blood flow.

Does peripheral angioplasty compromise limb blood flow?

Isotope limb blood flow studies were carried out using balloon, laser and Kensey catheter techniques to assess the outcome of peripheral angioplasty. Limb blood flow and Doppler ankle-brachial pressure measurements were obtained before angioplasty and at 6 months after angioplasty in a total of 101 angioplastied limbs: A fall in limb blood flow at 6 months was seen in 17% of the angioplastied limbs with no significant difference in the figures for the different types of angioplasty. Limb blood flow was also measured in 53 contralateral untreated limbs, approximately half of the patient group having both legs angioplastied. 25% of untreated limbs showed a fall in limb blood flow. Significantly more of the untreated limbs showed a fall in limb blood flow at 6 months where the contralateral, treated limb did not improve as a result of the angioplasty compared with those patients where the angioplastied leg improved. These results suggest that a lack of improvement in blood flow in the angioplastied limb may not result from failure of the angioplasty but may be the result of some factor, or combination of factors, which adversely affects both the angioplastied and the untreated leg in some patients.

A comparison of methods for estimating left ventricular volumes from radionuclide ventriculography.

An accurate reproducible measurement of left ventricular volume is important in the evaluation of cardiac disease. Four methods of left ventricular volume measurement by radionuclide ventriculography have been compared and their reproducibility assessed in a patient group. The methods studied were a geometric method, a method based on count data alone and two methods which require a blood sample and an estimate of ventricular depth. The accuracy of absolute volumes is difficult to determine due to the lack of a 'gold standard'. The method using count data alone was found to give reproducible results. Volumes can be calculated quickly and easily from data acquired in a standard radionuclide ventriculogram. End systolic volumes calculated using this method clearly separated normal and abnormal patient groups.

Value of a radionuclide limb blood flow technique in the assessment of percutaneous balloon and dynamic angioplasty.

In a prospective study, a radionuclide technique was used to evaluate the limb blood flow (LBF) changes in 30 patients undergoing dynamic (n = 15) or balloon (n = 15) angioplasty for arterial occlusions or stenoses, respectively. The results were compared with Doppler Ankle Brachial Index (DABI) and treadmill exercise tests. Whilst LBF values (ml of blood flow per 100 ml of limb volume per min) were significantly lower in limbs with arterial occlusion than stenosis (4.5 +/- 0.46 and 6.4 +/- 0.74, respectively; P less than 0.05). DABI provided no discrimination. Immediately after balloon angioplasty, there was a fall in DABI, from 0.60 +/- 0.05 to 0.47 +/- 0.04 (P less than 0.05), which rose 24 h later to 0.73 +/- 0.02 (P less than 0.01). Following dynamic angioplasty, DABI improved from 0.60 +/- 0.05 to 0.66 +/- 0.02 (P less than 0.05). At 3 weeks, the LBF improved from 4.6 +/- 0.66 to 11.1 +/- 0.53 (P less than 0.001) following dynamic angioplasty and from 6.2 +/- 0.68 to 8.53 +/- 0.81 (P less than 0.001) following balloon angioplasty. "Normal" LBF (greater than 10 ml/100 ml per min) was achieved in 80% of patients who underwent successful dynamic angioplasty but in only 36% of the balloon group (P less than 0.05, chi 2-test). Reproducibility of repeated LBF measurements in control limbs was superior to that of DABI. This was indicated by a lower coefficient of variation, 13.8% compared with 25.2%, and a higher correlation coefficient, r = 0.79 compared with 0.27. Treadmill exercise tests were invalid or impossible in 30% of all occasions.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of dobutamine stress thallium scintigraphy in the diagnosis of syndrome X.

Dobutamine stress thallium scintigraphy is a non-exercise stress technique used in the assessment of myocardial ischaemia. Non-exercise techniques are independent of the patient's exercise capacity or the subjective development of limiting symptoms. Preliminary data are presented regarding the effects of graded infusions of dobutamine (maximum 20 micrograms/kg/min) in seven consecutive patients with syndrome X. The dobutamine stress test caused significant increases in mean heart rate (rest 65.4 beats/min, peak dobutamine infusion 112.4 beats/min, P < 0.001) and systolic blood pressure (rest 138.6 mmHg, peak dobutamine infusion 166.7 mmHg, P = 0.002) and provoked typical symptoms in all the patients. Single photon emission computerized tomography was performed and the mean number of reversible defects was 1.86 per patient (range 1-3). One patient developed transient atrial fibrillation during the dobutamine infusion but there were no complications in the remainder of the study group. It is concluded that dobutamine-thallium scintigraphy in patients with syndrome X is safe, reproduces patients symptoms' reliably and presents a controllable degree of stress to the cardiovascular system. The consistent demonstration of a reversible perfusion defect in patients with syndrome X is evidence of abnormal myocardial physiology. This criterion could be added to those currently used to define syndrome X in order to improve objectively the identification of this patient group.