Two of the biochemical features of Alzheimers disease (AD) that contribute to neurodegeneration are intracellular oxidative stress and elevated levels of trace metal ions, especially Fe III , Cu II , and Zn II . [1] Both are factors involved in formation of the histological features in the brain used typically for postmortem diagnosis of AD, namely b-amyloid (Ab) plaques and neurofibrillary tangles. Therapeutic interventions under current investigation elsewhere include clioquinol [2] and desferrioxamine, [3] which are metal chelators that target elevated trace-metal ions in the brain, although neither are intended to affect oxidative stress directly and nor are they targeted to the brain. Antioxidant supplements have been studied separately as palliative-only measures for alleviation of the symptoms of AD.[4]Herein, we present for the first time a trifunctional approach to AD therapy. Modified and functionalized bidentate hydroxypyridinone pro-ligands (Scheme 1) address both the metal-ion and the oxidative imbalances inherent in AD while incorporating a glucose-receptor targeting feature.These prodrugs are designed to cross the blood-brain barrier (BBB), lose the pendant carbohydrate by enzymatic cleavage, passivate excess metal ions in the brain, and also protect neuronal cells against reactive oxygen species (ROS). Each of these functionalities has been demonstrated, thereby establishing the trifunctional principle as a valid goal in AD therapy. The prodrug strategy solves the potential problem of premature metal binding by using carbohydrates as both masking and directing substituents. In the context of increasing empirical support for re-establishing normal metal-ion homeostasis in neurodegenerative diseases, including AD, the trifunctional approach permits selective, tissue-dependent metal binding as a tailor-made, biologically compatible therapy.To demonstrate the utility of this approach, a series of assays on prototype compounds have been undertaken, including both in vitro and in vivo studies. This strategy is aimed at reducing neurodegeneration from oxidative stress; by passivating the pro-oxidant metal ions Fe III and Cu II , the production of ROS can be expected to be lower. By changing the R group on the pyridinone ring, the aqueous solubility, lipophilicity, and BBB permeability can be modified. Prodrug hydroxy (OH) groups have been elaborated by glycosylation (Scheme 1 b) such that, after enzymatic deprotection, the free ligands will have ring OH groups available that can either efficiently trap radicals or bind metal complexes (Scheme 1 a). Removing metal ions that promote Ab aggregation, such as Cu II and Zn II, also serves to prevent or reverse Scheme 1. Hydroxypyridinones: a) nonglycosylated pro-ligands and b) their glycosylated prodrug forms designed for metal passivation in the brain as a therapeutic intervention in Alzheimer's disease (AD).

No abstract

Glycosides of 3-hydroxy-4-pyridinones were synthesized and characterized by mass spectrometry, elemental analysis, (1)H and (13)C NMR spectroscopy, and in one case by X-ray crystallography. The Cu(2+) complex of a novel 3-hydroxy-4-pyridinone was synthesized and characterized by IR and X-ray crystallography, showing the ability of these compounds to chelate potentially toxic metal ions. An MTT cytotoxicity assay of a selected glycosylated compound showed a relatively low toxicity of IC(50) = 570 +/- 90 microM in a human breast cancer cell line. The pyridinone glycosides could be cleaved by a broad specificity beta-glycosidase, Agrobacterium sp.beta-glucosidase, and for one compound k(cat) and K(m) were determined to be 19.8 s(-1) and 1.52 mM, respectively. Trolox Equivalent Antioxidant Capacity (TEAC) values were determined for the free pyridinones, indicating the good antioxidant properties of these compounds. Metal-Abeta(1-40) aggregates with zinc and copper were resolubilized by the non-glycosylated pyridinone ligands.

The complete array of those hydrotris(pyrazolyl/thioimidazolyl)borate ligands that were developed and used in the author's laboratories, with N3, N2S, NS2, and S3 donor sets, was scanned for their ability to form Zn-OH2 and Zn-OH complexes. The coordination motifs found were Zn-OH2, Zn-OH, Zn-OH-Zn, and Zn-O2H3-Zn. Of these, the well-established Zn-OH motif was complemented with novel species bearing N3, NS2, and S3 tripods. The Zn-OH2 motif was observed only with pyrazolylborate ligands and only in unusual situations with coordination numbers higher than 4 for zinc. The new Zn-OH-Zn motif was realized for three different pyrazolylborates, for one NS2 tripod, and for two S3 tripods. Finally, it was verified that the Zn-O2H3-Zn motif again occurs only with pyrazolylborate ligands. The new complexes were identified by a total of 11 structure determinations.

Two of the biochemical features of Alzheimers disease (AD) that contribute to neurodegeneration are intracellular oxidative stress and elevated levels of trace metal ions, especially Fe III , Cu II , and Zn II . [1] Both are factors involved in formation of the histological features in the brain used typically for postmortem diagnosis of AD, namely b-amyloid (Ab) plaques and neurofibrillary tangles. Therapeutic interventions under current investigation elsewhere include clioquinol [2] and desferrioxamine, [3] which are metal chelators that target elevated trace-metal ions in the brain, although neither are intended to affect oxidative stress directly and nor are they targeted to the brain. Antioxidant supplements have been studied separately as palliative-only measures for alleviation of the symptoms of AD.[4]Herein, we present for the first time a trifunctional approach to AD therapy. Modified and functionalized bidentate hydroxypyridinone pro-ligands (Scheme 1) address both the metal-ion and the oxidative imbalances inherent in AD while incorporating a glucose-receptor targeting feature.These prodrugs are designed to cross the blood-brain barrier (BBB), lose the pendant carbohydrate by enzymatic cleavage, passivate excess metal ions in the brain, and also protect neuronal cells against reactive oxygen species (ROS). Each of these functionalities has been demonstrated, thereby establishing the trifunctional principle as a valid goal in AD therapy. The prodrug strategy solves the potential problem of premature metal binding by using carbohydrates as both masking and directing substituents. In the context of increasing empirical support for re-establishing normal metal-ion homeostasis in neurodegenerative diseases, including AD, the trifunctional approach permits selective, tissue-dependent metal binding as a tailor-made, biologically compatible therapy.To demonstrate the utility of this approach, a series of assays on prototype compounds have been undertaken, including both in vitro and in vivo studies. This strategy is aimed at reducing neurodegeneration from oxidative stress; by passivating the pro-oxidant metal ions Fe III and Cu II , the production of ROS can be expected to be lower. By changing the R group on the pyridinone ring, the aqueous solubility, lipophilicity, and BBB permeability can be modified. Prodrug hydroxy (OH) groups have been elaborated by glycosylation (Scheme 1 b) such that, after enzymatic deprotection, the free ligands will have ring OH groups available that can either efficiently trap radicals or bind metal complexes (Scheme 1 a). Removing metal ions that promote Ab aggregation, such as Cu II and Zn II, also serves to prevent or reverse Scheme 1. Hydroxypyridinones: a) nonglycosylated pro-ligands and b) their glycosylated prodrug forms designed for metal passivation in the brain as a therapeutic intervention in Alzheimer's disease (AD).