Dissertation/Thesis Abstract

Progress towards medical bioremediation by enzymatic transformation of 7-ketocholesterol and the pyridinium bisretinoid A2E
by Schloendorn, John, Ph.D., Arizona State University, 2009, 152; 3392127
Abstract (Summary)

A major feature of aging is the accumulation of certain recalcitrant molecules inside cells and their lysosomes as organisms grow older. These metabolic end products cannot be adequately removed or degraded by any known human enzymes, and they may contribute to or cause disease if they exceed a tolerable threshold. First, cholesterol and its oxidized derivatives (such as 7-Ketocholesterol (7KC)) accumulate in the artery lining, and they are implicated in atherosclerosis. Second, condensation reactions of sugars with proteins can give rise to advanced glycation end-products (AGE), such as N-E-carboxymethyllysine (CML), which are implicated in aging and diabetes. Third, carotenoid lipofuscin (featuring compounds such as the pyridinium bisretinoid A2E) accumulates in the retinal pigment epithelium, and it is implicated in age-related macular degeneration.

Medical Bioremediation is the novel proposal to treat all these storage disorders with enzymes from organisms that can break these substances down. This work contains the first detailed description of microbes with the ability to degrade 7KC. Most of these species initiate the breakdown with a reaction analogous to cholesterol oxidase. A preliminary toxicity study showed that this metabolite is less toxic to cultured human cells than is 7KC.

Biodegradation of CML has not previously been studied. This work describes the first isolation of microbes with the ability to degrade CML from environmental samples. A functional-metagenomic approach was used in an attempt to discover any genes present in these cultures for the production of lysine from CML. Even though almost a trillion base pairs were searched, no such genes were discovered.

Database searches and theoretical prediction led to the discovery of the first known A2E-degrading enzymes. The enzymes came from two classes, the carotenoid cleavage oxygenases (CCO) and the peroxidase/laccase family, which degraded A2E with different efficiencies. The CCOs perform a single, defined cleavage according to their built-in specificity. The peroxidases completely destroyed the molecule by step-wise oxidation of its many conjugated double bonds. A peroxidase was delivered to cultured retinal pigment epithelial lysosomes by a collaborator, and it safely degraded A2E there.

Overall, this work provides an early-stage proof of concept of Medical Bioremediation.

Indexing (document details)
School: Arizona State University
School Location: United States -- Arizona
Source: DAI-B 71/01, Dissertation Abstracts International
Subjects: Molecular biology
Keywords: Bioremediation, Ketocholesterol, Macular degeneration, Pyridinium bisretinoid
Publication Number: 3392127
ISBN: 978-1-109-57564-4
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