Nuclear medicine in the assessment of differentiated thyroid cancer.

Despite modern multi-modality treatment, 10-30% of patients treated for differentiated thyroid cancer (DTC) ultimately develop local recurrence or metastatic disease. These malignancies are frequently slow-growing and secondary surgical resection is often undertaken along with radioactive iodine treatment. Correlation of radiological imaging with nuclear medicine studies is essential for individualized treatment planning, and to optimize this management. Radiologists should be familiar with the interpretation of various nuclear medicine studies used to image differentiated thyroid neoplasms.

Imaging in the investigation of paraneoplastic syndromes.

Paraneoplastic syndromes are a heterogeneous group of disease presentations caused by underlying tumours. As they are non-metastatic in nature an intensive diagnostic evaluation is warranted to identify potentially curable lesions. The selection of the appropriate method of imaging is important in these cases, especially when history and physical examination are unrevealing. In this review the important paraneoplastic syndromes and underlying malignancies are discussed along with relevant imaging strategies.

Method to sensitize bacterial spores to subsequent killing by dry heat or ultraviolet irradiation.

Hydrogen peroxide and ultraviolet irradiation are known to interact synergistically for killing of bacterial spores. Synergy could be demonstrated with spores of Bacillus megaterium ATCC19213 adsorbed to filter paper strips or glass coverslips treated first with the peroxide and then dried for as long as 48 h prior to UV irradiation. This delayed action was considered to be due to absorption of the peroxide by the spores in an active but not readily vaporized form, which could become sporicidal also if the spores were heated to 50 degrees C. B. megaterium spores mixed with 0.1% (32.6 mM) H(2)O(2) solution appeared to absorb as much as 15 micromol/mg dry weight or about 0.5 mg/mg, but only a third to half of the peroxide could be recovered by water washing. A part of the unrecovered peroxide was degraded in reactions resulting in measurable production of oxygen. Degradation was not reduced by heating the spores to 65 degrees C or by azide and so appeared to be non-enzymatic. Spores of the anaerobe Clostridium sporogenes were also sensitized to ultraviolet killing by H(2)O(2) treatment followed by drying. They appear to absorb less peroxide, only about 2 micromol/mg, but had lower capacities to degrade H(2)O(2) so that nearly all of the peroxide could be recovered by washing with water. The findings presented should be helpful in the design of new methods for synergistic killing of spores by H(2)O(2) and UV irradiation or dry heat, especially involving, for example, packaging materials.

Membrane locus and pH sensitivity of paraben inhibition of alkali production by oral streptococci.

Parabens were found to be potent inhibitors of alkali production from arginine by oral streptococci such as Streptococcus rattus, Streptococcus sanguis and Streptococcus gordonii. For example, 2 mumol butylparaben per ml completely and irreversibly inhibited arginolysis by intact cells of S. rattus FA-1 and was lethal for the organism. In contrast, butylparaben was not a very effective inhibitor of ureolysis by intact cells of Streptococcus salivarius 57.I, although it did kill the cells. Butylparaben irreversibly inhibited the cytoplasmic enzymes arginine deiminase, carbamate kinase and urease in permeabilized cells or isolated form. However, inhibition of arginolysis by intact cells appeared to be due primarily to irreversible inhibition of transport systems for arginine uptake, because butylparaben added to intact cells did not reduce levels of arginine deiminase when the cells were subsequently permeabilized after washing. The insensitivity of ureolysis by intact cells to butylparaben can be related to the known high permeability of cell membranes to urea and the cytoplasmic location of urease. The potency of butylparaben as an inhibitior of arginolysis or glycolysis and as a lethal agent was found to be greater at acid pH that at neutral or alkaline pH.

Inactivation of enzymes within spores of Bacillus megaterium ATCC 19213 by hydroperoxides.

The organic hydroperoxides t-butyl hydroperoxide, cumene hydroperoxide, and peracetic acid were found to act similarly to hydrogen peroxide in causing inactivation of enzymes within intact spores of bacillus megaterium ATCC 19213 concomitant with mortality. Spores treated with lethal levels of the agents were germinated and permeabilized for enzyme assays. The hierarchy of sensitivities among enolase, glucose-6-phosphate dehydrogenase (G6Pdh), and pyruvate kinase to inactivation varied somewhat with the specific hydroperoxide used, possibly because of the differences in the types of radicals generated. However, each agent inactivated each of the enzymes, albeit at different rates. Comparative assessments of enzyme inactivation by lethal levels of H2O2 or by moist heat showed that some enzymes, such as G6Pdh, are highly sensitive to inactivation, while others, such as ATPases, are much more resistant. The enzymes G6Pdh and aldolase were highly sensitive to hydroperoxide inactivation and also to moist heat, while pyruvate kinase was much more sensitive to hydroperoxides than to moist heat. Our overall interpretation of the findings is that hydroperoxides and moist heat can produce cumulative damage to sensitive enzymes within spores, which progressively diminishes the capacities of the cells to undergo the outgrowth required for return to vegetative life.

Turning on and turning off the arginine deiminase system in oral streptococci.

The arginine deiminase system in oral streptococci is highly regulated. It requires induction and is repressed by catabolites such as glucose or by aeration. A comparative study of regulation of the system in Streptococcus gordonii ATCC 10558, Streptococcus rattus FA-1, and Streptococcus sanguis NCTC 10904 showed an increase in activity of the system in S. sanguis of some 1467-fold associated with induction-depression of cells previously uninduced-repressed. The activity of the system was assayed in terms of levels of arginine deiminase, the signature enzyme of the system, in permeabilized cells. Increases in enzyme levels associated with induction-depression were less for the other two organisms, mainly because of less severe repression, especially for S. rattus FA-1, which was the least sensitive to catabolite repression or aeration. Regulation of the arginine deiminase system involving induction and catabolite repression was demonstrated also with monoorganism biofilms composed of cells of S. sanguis adherent to glass slides. Fully uninduced-repressed cells from suspension cultures or biofilms were compromised in their abilities to catabolize arginine to protect themselves against acid damage. However, it was found that the system can be rapidly turned on or turned off, although induction-depression did appear to require cell growth. Still, the system could respond rapidly to the availability of arginine to reestablish high capacity for alkali production.

Sporicidal action of peracetic acid and protective effects of transition metal ions.

Although peracetic acid (PAA) is used widely for cold sterilization and disinfection, its mechanisms of sporicidal action are poorly understood. PAA at high concentrations (5-10%) can cause major loss of optical absorbance and microscopically-visible damage to bacterial spores. Spores killed by lower levels of PAA (0.02-0.05%) showed no visible damage and remained refractile. Treatment of spores of Bacillus megaterium ATCC 19213 with PAA at concentrations close to the lethal level sensitized the cells to subsequent heat killing. In addition, PAA was found to act in concert with hypochlorite and iodine to kill spores. Antioxidant sulfhydryl compounds or ascorbate protected spores against PAA killing. Trolox, a water-soluble form of alpha-tocopherol, was somewhat protective, while other antioxidants, including alpha-tocopherol, urate, bilirubin, ampicillin and ethanol were not protective. Chelators, including dipicolinate, were not protective, but transition metal ions, especially the reduced forms (Co2+, Cu+ and Fe2+) were highly protective. The net conclusions are that organic radicals formed from PAA are sporicidal and that they may act as reducing agents for spores that are normally in a highly oxidized state, in addition to their well known actions as oxidizing agents in causing damage to vegetative cells.