Michael A. Davis

New Tn10 derivatives for transposon mutagenesis and for construction of lacZ operon fusions by transposition

We describe below several new variants of the tetracycline-resistance transposon Tn10 which are more useful than the wild-type transposon for many types of genetic and physical analysis of bacteria. These derivatives have one or more of the following new properties: (i) new drug resistance markers; (ii) high transposition frequencies; (iii) removal of the transposase gene to a position outside of the transposing segment; (iv) internal deletions which eliminate the ability of Tn10 to make adjacent deletion/inversions; or (v) addition of a trp-lac operon fusion segment just inside one terminus such that insertion can automatically generate a transcriptional fusion to the interrupted operon. Phage and plasmid vehicles carrying these new elements are described.

Pulmonary distribution of particles given by intratracheal instillation or by aerosol inhalation

Abstract In animal studies concerned with the deposition of particulate matter in the lung, two methods for delivery of particles are commonly used, aerosol inhalation and intratracheal instillation of particle suspensions. We have attempted to evaluate the distribution patterns of each of these methods. Particles labeled with 99m Tc were administered to both rats and hamsters. The animals were subsequently killed. The lungs were excised, weighed, inflated, dried, and divided into 54 pieces which were counted individually in a Nuclear-Chicago Model 4230 Automatic Gamma Scintillation System. Groups receiving intratracheal instillations demonstrated nonuniform distribution patterns with preferential deposition in the dependent portions of the lung. The aerosol groups evidence more even distribution with preferential deposition in the apical lobes.

Comparison Between the Effects of Nitroprusside and Nitroglycerin on Ischemic Injury during Acute Myocardial Infarction

SUMMARY This clinical and experimental investigation was designed to delineate and compare the relative effects of sodium nitroprusside (NP) and nitroglycerin (TNG) on electrocardiographic ischemic injury following acute myocardial infarction in patients and following coronary artery occlusion in dogs. Accordingy, in ten patients with anterior acute myocardial infarction and ST-segment elevation stable for 60 min, the effects ofNP (average 95 4g/min i.v.) and TNG (average 0.48 mg sublingually) were studied. The hemodynamic actions of NP and TNG were directionally similar. However, NP increased average ST-segment elevation (ST) by 2.0 ± 0.2 mm, while TNG reduced ST by 1.4 ± 0.4 mm. In order to clarify this disparity, coronary artery occlusions were carried out in 14 open-chest dogs. During control, NP and TNG time periods, epicardial electrograms were recorded and regional myocardial blood flow (RMBF) determined by the microsphe te N side increased ST-egment elevation from 4.6 ± 0.6 to 5.7 ± 0.6 mV (P < 0.05) and reduced RMBF from 35± 3 to 27 ± 2 mI/uul/100 g (P < 0.01) in the ischemic zones. In contrs, TNG reced; STsegment elevation from 4.9 ± 0.7 to 3.0 ± 0.7 mV (P < 0.05), Wle increasing RMBF to 43 ± 4 ml/mi/100 g (P < 0.05) and the endo/ epicardial ratio from 0.57 ± 0.06 to 0.69 ± 0.07 (P < 0.01). Although TNG and NP exhibit similar hemodynamic effects, TNG reduced electrocardiographic ischemic injury, at least in part, by increasing perfusion of the ischemic areas and redistriutng it favorably, while NP increased electrocardiographic iscbemic injury, at least in part, by reducing perfusion. Therefore, TNG seems preferable to NP for reducing preload and afterload in ts during the early phase of acute myocardial infarction.

Bone scanning: Radionuclidic reaction mechanisms

One of the major successes of nuclear medicine in recent years has been the clinical utility of the 99mTc-labeled bone-imaging agents. This article is concerned with the evidence available for the mechanisms by which these and other such radiopharmaceuticals localize at sites in the skeleton.

Comparison of 99mTc-labeled phosphate and phosphonate agents for skeletal imaging

The use of 99mTc-labeled phosphate and phosphonate compounds in place of 18F, 85Sr, and 87Sr for bone scintigraphy has become commonplace throughout the world in a relatively short time. The labeling of polyphosphate with 99mTc 4 years ago, followed rapidly by the introduction of 99mTc-labeled pyrophosphate for skeletal imaging, must therefore be regarded as a major contribution to the practice of diagnostic nuclear medicine. The markedly reduced patient radiation exposure and concomitant increase in photon detection efficiency derived from the more favorable physical decay characteristics of 99mTc led to increased sensitivity and resolution and in turn to improved diagnostic efficacy. The subsequent clinical use of the phosphonate complex 99mTc-HEDP represented a further modification of the same basic approach. Current clinical trials with 99mTc-labeled methylene diphosphonic acid (MDP), which appears to demonstrate enhanced biologic properties for scintigraphy of the osseous structures, is the latest example in this series of refinements. This article compares the technetium-labeled agents already in clinical use and, using animal data, contrasts them with several new multifunctional phosphonates and the novel inorganic compound sodium imidodiphosphate (IDP). In addition, an attempt is made to clarify the conflicting evidence in the nuclear medicine literature regarding the relationship between polyphosphate chain length and skeletal uptake.

Clinical risk factors for the development of hypertension in patients treated with inhibitors of the VEGF signaling pathway

VEGF signaling pathway inhibitor (anti‐VEGF) therapy is associated with hypertension, but little is known about predisposing clinical characteristics. This study describes the real‐world association between baseline clinical characteristics, blood pressure (BP) response, and survival in patients prescribed anti‐VEGF therapies.

In vivo 19F NMR imaging of liver, tumor, and abscess in rats. Preliminary results.

In vivo magnetic resonance imaging (MRI) has employed almost exclusively the proton because of its high gyromagnetic ratio and natural abundance relative to other nuclei. Recent research has focused on imaging using nuclei other than 1H, but has been limited by the decreased sensitivity and/or low biologic concentrations of the nuclei. Fluorine (19F), with a gyromagnetic ratio second only to that of hydrogen, is a theoretically attractive nucleus for MRI, but fluorine is present in only minute amounts in most tissues. Perfluorochemical emulsions (PFC), developed as blood replacement agents, appear to be safe vehicles for fluorine administration. We report our initial results of in vivo 19F magnetic resonance imaging of liver, tumor, and abscess in rats given exogenous fluorine.

Liposomes carrying diatrizoate. Characterization of biophysical properties and imaging applications.

We have prepared and characterized a suspension of liposomes carrying diatrizoate. Vesicles were made with egg lecithin, cholesterol, and stearylamine in a 4:1:1 molar ratio, and contained meglumine sodium diatrizoate in their aqueous phase. They ranged up to 2.0 microns in size and had a multilamellar structure. These vesicles were then injected into normal and tumor-bearing rats, as well as normal dogs and a baboon. The iodine component proved to have a prolonged blood pool residence time, was cleared through reticuloendothelial and urinary tissues, and was completely excreted within seven days. The LD50 in mice was 2.3 g I/kg (38.5 g of liposome suspension/kg). Imaging studies with diatrizoate-carrying liposomes demonstrated marked and prolonged contrast enhancement of blood pool, liver, spleen, kidneys, urine, and tumor rims. Furthermore, the blood, liver, and spleen opacification was greater and longer sustained than when an equivalent amount of iodine in free diatrizoate was used. These diatrizoate-carrying liposomes are particularly well suited for computed tomographic imaging of blood pool and reticuloendothelial structures.

The preparation and characterization of liposomes containing X-ray contrast agents

Unilamellar phospholipid vesicles loaded with the water-soluble, ionic X-ray contrast agent diatrizoate (Hypaque, Renografin) were manufactured by reverse-phase evaporation for use as organ-enhancing agents in X-ray computed tomography. Encapsulation efficiency was determined as a function of various diatrizoate concentrations in vesicles of varying lipid composition. Loss of encapsulated diatrizoate over 24 h was examined in vesicles composed of several egg phosphatidylcholine/cholesterol ratios. Size estimates for loaded vesicles were obtained by negative-stain electron microscopy, Millipore filtration and light microscopy. Intravenous in vivo injection of loaded vesicles in the rat resulted in significant enhancement of both spleen and liver on subsequent scans. Vesicles were similarly prepared with the water-soluble, nonionic agent metrizamide (Amipaque). Encapsulation efficiency was determined, and in vivo behavior was observed.

Heavy Metal Particulate Contrast Materials for Computed Tomography of the Liver

Silver iodide colloid was used as a model of a particulate hepatic contrast agent for computed tomography (CT). Following intravenous administration to rabbits, approximately 90% of the injected dose was phagocytized by the livers reticuloendothelial system, resulting in a four- to five-fold increase in the liver CT number. Suspensions of CeO2. Dy2O3. and Gd2O3, were prepared using stabilizers to prevent clumping. Particles of appropriate size for reticuloendothelial cell uptake were selected by centrifugation. Intravenous injections of the three suspensions increased the CT number of rabbit liver by approximately 30 Hounsfield units (HU: 1,000 scale) for each milligram of contrast material per gram of liver. An injected dose of 1 g of each experimental contrast agent resulted in a minimum addition of 250 HU to the liver CT number. A linear relationship was found between the CT number and its contrast material concentration. This relationship was also tested In vitro by ashing samples of livers containing various amounts of contrast material. Standard curves of CT number versus contrast material concentration in the liver were plotted, which predicted the amount of liver enhancement obtained after contrast material injection. There may be a use for heavy metal-containing particulate materials as hepatic contrast agents, since they opacify the liver more selectively, to a higher degree, and for longer periods than the conventional biliary and urographic iodinated contrast materials.