Transmission of prions

The "protein only" hypothesis states that the infectious agent causing transmissible spongiform encephalopathies is a conformational isomer of PrP, a host protein predominantly expressed in brain, and is strongly supported by many lines of evidence. Prion diseases are so far unique among conformational diseases in that they are transmissible, not only experimentally but also by natural routes, mainly by ingestion. A striking feature of prions is their extraordinary resistance to conventional sterilization procedures, and their capacity to bind to surfaces of metal and plastic without losing infectivity. This property, first observed in a clinical setting, is now being investigated in experimental settings, both in animals and in cell culture.     

Transmission of prions

The "protein only" hypothesis holds that the infectious agent causing transmissible spongiform encephalopathies is a conformational isomer of PrP, a host protein that is predominantly expressed in the brain. This hypothesis is strongly supported by many lines of evidence. To date, prion diseases are unique among conformational diseases in that they are transmissible-experimentally and by natural routes (mainly by ingestion). The pathway of prions to the brain has been elucidated in outline. A striking feature of prions is their extraordinary resistance to conventional sterilization procedures and their capacity to bind to surfaces of metal and plastic without losing infectivity. This property, first observed in a clinical setting, is now being investigated in experimental settings, both in animals and in cell culture.     

Membrane fusion: studies with a calcium-sensitive dye, arsenazo III, in liposomes.

Fusion between vesicles, cells, or organelles may be defined as confluence of two membrane-bound compartments without access of their solutes to external milieu. To study fusion by this criterion, we have trapped the metallochromic calcium-sensitive dye, arsenazo III (AIII), partially calcium-saturated (AIII-Ca) in one population of liposomes (phoshatidylcholine 90:dicetylphosphate 10), and ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetate (EGTA) in a second. In such mixtures, interaction of EGTA with AIII-Ca was measured by a large color shift from blue leads to red (decreased absorbance at 660 nm). Fusion of liposomes (but also lysis and diffusion across the membranes) was proportional to these decrements. The exogenous "fusogens," lysolecithin and retinol, were added to liposomes for 5-24 hr at 37 degrees; after rechromatography, measurements were made of total dye, fraction of dye converted from AIII-Ca to AIII, and total lipid. After correction for lysis and diffusion, lysolecithin (200 microng/ml) induced 23% fusion (volume of AIII liposomes confluent with EGTA liposomes) and retinol (300 microng/ml) induced 15%. With one molar percent cortisol (a membrane stabilizer) in the liposome membranes, fusion induced by fusogens was reduced 2-fold. Neither multi-nor unilamellar liposomes fused with each other in the absence of exogenous fusogens, despite wide variations in molar lipid ratios. Results suggest that liposome-liposome fusion is a slow process requiring exogenous fusogens, which may depend upon contributions of other membrane constituents to mimic closely the fusion of natural membranes.     

Prostaglandins,thromboxanes, and polymorphonuclear leukocytes

When appropriately stimulated (even in the absence of phagocytosis), human polymorphonuclear leukocytes release and/or generate proinflammatory materials and substances capable of provoking tissue injury. These include hydrolases and nonenzymatic substances ordinarily contained within lysosomes, as well as oxygen-derived free radicals. It is now possible to add prostaglandins and thromboxanes to this list. Whereas prostaglandins are capable of eliciting many phenomena associated with inflammation, their effects on cyclic nucleotide metabolism may render these compounds antiinflammatory. Thus, the very cells that release mediators of inflammation provide a mechanism for modulating the inflammatory response.This work was supported in part by grants from the National Institutes of Health (AM-18531, AM-11949 and HL-15140) and Whitehall, National, and National Science, Foundations.Dr. Goldstein is the recipient of a Career Scientist Award from the Irma T. Hirschl Trust.     

Steroids,aspirin, and inflammation

The ability of adrenal corticosteroids to both suppress inflammation and compromise host defenses has been well documented. Recently, a series of in vitro and in vivo experiments, based on our new knowledge of the cell biology of inflammation and the biochemistry of the phagocytic cell itself, has provided new insights into the mechanism of steroid action in the inflammatory process. Evidence is presented thatpharmacologic doses of steroids are capable of inhibiting each of the steps in phagocytic-microorganism interaction: chemotaxis, recognition and opsonization, phagocytosis, membrane fusion, and degranulation. In addition, steroid alteration of the postphagocytic superoxide production, hydrogen peroxide generation, and prostaglandin and thromboxane synthesis is described. The antiinflammatory effects of aspirin and indomethacin can be explained almost entirely by virtue of their ability to inhibit cyclooxygenase, this preventing the transformation of arachidonic acid to both prostaglandins and thromboxanes. The cortisol-induced inhibition of endoperoxides, prostaglandins, and thromboxanes (at a site proximal to the release of arachidonic acid) may well explain those antiinflammatory actions that cortisone shares with aspirin. However, patients treated with nonsteroidal antiinflammatory agents effectively combat infections. In contrast, corticosteroids have more profound effects, as can be seen by the inhibition of superoxide production, with the subsequent decrease in hydrogen peroxide generation and the diminution in release of the antibacterial lysosomal hydrolases within the phagocytic vacuole. Thus, corticosteroids interfere with the killing of microorganisms. This new understanding of the pharmacologie action of cortisol on phagocytic cells explains, we believe, how glucocorticoids alleviate inflammation while, at the same time, they permit multiplication of the offending microorganism within the phagocyte.Aided by grants (AM-11949, HL-19072, HL-19721, GM-23211) from the National Institutes of Health, The National Foundation-March of Dimes, The National Science Foundation (76-05621), The Whitehall Foundation, and The Arthritis Foundation.     

Tyrosine hydroxylase expression within Balb/C and C57Black/6 mouse locus coeruleus. I. Topological organization and phenotypic plasticity of the enzyme-containing cell population

Tyrosine hydroxylase phenotype expression was investigated in the catecholaminergic population of the locus coeruleus neurons of two pure inbred mouse strains, Balb/C and C57Black/6. Therefore, we have characterized the precise organization of tyrosine hydroxylase-expressing perikarya population, in control animals and following RU24722 treatment, which is known to induce tyrosine hydroxylase expression. Serial coronal sections were selected along the caudo-rostral extent of the structure and were processed for tyrosine hydroxylase immunocytochemistry. Three days after the treatment, an increase in the number of cells which expressed tyrosine hydroxylase was observed all along the locus coeruleus in the Balb/C strain only. This increase equalized the catecholaminergic neuron populations of the two strains. In the caudal subdivision of the structure, these newly detected perikarya were intermingled with the perikarya which expressed tyrosine hydroxylase in control conditions. In the rostral half, the additional immnunoreactive perikarya enlarged the mean coerulean space, defined as the area delimited by the tyrosine hydroxylase-containing perikarya. These results demonstrate a plasticity of the tyrosine hydroxylase phenotype expression, topologically organized and specific to the Balb/C strain.