Biological and electron microscopic changes in gamma radiated Cryptococcus neoformans

Dembitzer, Herbert M.; Buza, I.; Reiss, Frederick

doi:10.1007/bf02051669

Cited by 15 publications

(10 citation statements)

References 7 publications

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“…Dembintzer et al reported the disappearance of the polysaccharide capsule after irradiation of C. neoformans with gamma rays (16). However, that study employed lethal radiation doses (6,000 to 10,000 Gy) for C. neoformans (14) and reported no measurements of the capsule size.…”

Section: Discussionmentioning

confidence: 99%

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Radiological Studies Reveal Radial Differences in the Architecture of the Polysaccharide Capsule ofCryptococcus neoformans

Bryan¹,

Zaragoza

Zhang³

et al. 2005

Eukaryot Cell

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The polysaccharide capsule of the pathogenic fungus Cryptococcus neoformans is an important virulence factor, but relatively little is known about its architecture. We applied a combination of radiological, chemical, and serological methods to investigate the structure of this polysaccharide capsule. Exposure of C. neoformans cells to gamma radiation, dimethyl sulfoxide, or radiolabeled monoclonal antibody removed a significant part of the capsule. Short intervals of gamma irradiation removed the outer portion of the cryptococcal capsule without killing cells, which could subsequently repair their capsules. Survival analysis of irradiated wild-type, acapsular mutant, and complemented mutant strains demonstrated that the capsule contributed to radioprotection and had a linear attenuation coefficient higher than that of lead. The capsule portions remaining after dimethyl sulfoxide or gamma radiation treatment were comparable in size, 65 to 66 m 3 , and retained immunoreactivity for a monoclonal antibody to glucuronoxylomannan. Simultaneous or sequential treatment of the cells with dimethyl sulfoxide and radiation removed the remaining capsule so that it was not visible by light microscopy. The capsule could be protected against radiation by either of the free radical scavengers ascorbic acid and sorbitol. Sugar composition analysis of polysaccharide removed from the outer and inner parts of the capsule revealed significant differences in glucuronic acid and xylose molar ratios, implying differences in the chemical structure of the constituent polysaccharides. Our results provide compelling evidence for the existence of two zones in the C. neoformans capsule that differ in susceptibility to dimethyl sulfoxide and radiation and, possibly, in packing and composition.

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Section: Discussionmentioning

confidence: 99%

“…Three decades ago Dembintzer et al reported the phenomenon of C. neoformans capsule disappearance after irradiation with large doses of gamma rays (16). We hypothesized that by using much lower doses of radiation, we could use this nonchemical method for removing the capsule gradually and thus study its structure.…”

mentioning

confidence: 98%

Radiological Studies Reveal Radial Differences in the Architecture of the Polysaccharide Capsule ofCryptococcus neoformans

Bryan¹,

Zaragoza

Zhang³

et al. 2005

Eukaryot Cell

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“…In the early 1970s, it was reported that extremely high doses of gamma radiation greatly reduced the size of the C. neoformans capsule (16), but this phenomenon was largely forgotten until recently, when it was rediscovered and examined in detail (6). Doses of gamma radiation that are thousands of times lower than those previously described (16) release capsular polysaccharide very efficiently, by a presumed mechanism involving the creation of free radicals from solution (6).…”

mentioning

confidence: 99%

Radial Mass Density, Charge, and Epitope Distribution in theCryptococcus neoformansCapsule

Maxson¹,

Dadachova

Casadevall³

et al. 2007

Eukaryot Cell

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Exposure of Cryptococcus neoformans cells to gamma radiation results in a gradual release of capsular polysaccharide, in a dose-dependent manner. This method allows the systematic exploration of different capsular regions. Using this methodology, capsule density was determined to change according to the radial distribution of glucuronoxylomannan and total polysaccharide, becoming denser at the inner regions of the capsule. Scanning electron microscopy of cells following gamma radiation treatment confirmed this finding. The zeta potential of the capsule also increased as the capsule size decreased. However, neither charge nor density differences were correlated with any change in sugar composition (xylose, mannose, and glucuronic acid) in the different capsular regions, since the proportions of these sugars remained constant throughout the capsule. Analysis of the capsular antigenic properties by monoclonal antibody binding and Scatchard analysis revealed fluctuations in the binding affinity within the capsule but not in the number of antibody binding sites, suggesting that the spatial organization of high-and low-affinity epitopes within the capsule changed according to radial position. Finally, evidence is presented that the structure of the capsule changes with capsule age, since the capsule of older cells became more resistant to gamma radiation-induced ablation. In summary, the capsule of C. neoformans is heterogeneous in its spatial distribution and changes with age. Furthermore, our results suggest several mechanisms by which the capsule may protect the fungal cell against exogenous environmental factors.Capsules are a common feature among microorganisms, especially pathogenic bacteria such as Bacillus anthracis, Streptococcus pneumoniae, and Neisseria meningitidis. Microbial capsules can confer particular characteristics, such as protection against stress conditions (64), and are prominent virulence factors. In contrast to the situation in bacteria, extracellular capsules are rare in fungi. The only encapsulated pathogenic fungus is the basidiomycetous yeast Cryptococcus neoformans. This fungus is commonly found in the environment, inhabiting various niches such as pigeon droppings, trees, and water (reviewed in reference 8). The pathogenesis of C. neoformans has been well studied. The yeast is commonly acquired by the host via inhalation. The infection is asymptomatic in immunocompetent hosts. However, in cases of immune suppression, pulmonary infection can be followed by extrapulmonary dissemination of the yeast into other organs, such as spleen, liver, and brain. Untreated cryptococcal meningitis is invariably fatal.The polysaccharide capsule of C. neoformans is considered the main virulence factor of this pathogen (37). Acapsular C. neoformans strains manifest greatly reduced virulence (10, 31), and mutants that produce a larger capsule are hypervirulent (19). The capsule of this yeast is believed to function in protection from desiccation, radiation, and predation by phagocytic organisms (reviewed in...

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“…R adiation possesses microbicidal properties and ␥-irradiation is routinely used for the sterilization of medical supplies and certain foods. Ionizing radiation such as ␥-rays, ␤-particles, and especially ␣-particles from external sources can kill different strains of bacteria and fungi such as Escherichia coli, Cryptococcus neoformans (CN), and Mycobacterium tuberculosis (1)(2)(3). Despite its microbicidal properties, radiation is not used in current antimicrobial therapy.…”

mentioning

confidence: 99%

Ionizing radiation delivered by specific antibody is therapeutic against a fungal infection

Dadachova

Nakouzi

Bryan³

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

100

115

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There is an urgent need for new antimicrobial therapies to combat drug resistance, new pathogens, and the relative inefficacy of current therapy in compromised hosts. Ionizing radiation can kill microorganisms quickly and efficiently, but this modality has not been exploited as a therapeutic antimicrobial strategy. We have developed methods to target ionizing radiation to a fungal cell by labeling a specific mAb with the therapeutic radioisotopes Rhenium-188 and Bismuth-213. Radiolabeled antibody killed cells of human pathogenic fungus Cryptococcus neoformans in vitro, thus converting an antibody with no inherent antifungal activity into a microbicidal molecule. Administration of radiolabeled antibody to mice with C. neoformans infection delivered 213 Bi and 188 Re to the sites of infection, reduced their organ fungal burden, and significantly prolonged their survival without apparent toxicity. This study establishes the principle that targeted radiation can be used for the therapy of an infectious disease, and suggests that it may have wide applicability as an antimicrobial strategy.

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Biological and electron microscopic changes in gamma radiated Cryptococcus neoformans

Cited by 15 publications

References 7 publications

Radiological Studies Reveal Radial Differences in the Architecture of the Polysaccharide Capsule ofCryptococcus neoformans

Radiological Studies Reveal Radial Differences in the Architecture of the Polysaccharide Capsule ofCryptococcus neoformans

Radial Mass Density, Charge, and Epitope Distribution in theCryptococcus neoformansCapsule

Ionizing radiation delivered by specific antibody is therapeutic against a fungal infection

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