rolitetracycline and Alzheimer-Disease

Alzheimer disease is characterized by the abnormal aggregation of amyloid beta peptide into extracellular fibrillar deposits known as amyloid plaques. Soluble oligomers have been observed at early time points preceding fibril formation, and these oligomers have been implicated as the primary pathological species rather than the mature fibrils. A significant issue that remains to be resolved is whether amyloid oligomers are an obligate intermediate on the pathway to fibril formation or represent an alternate assembly pathway that may or may not lead to fiber formation. To determine whether amyloid beta oligomers are obligate intermediates in the fibrillization pathway, we characterized the mechanism of action of amyloid beta aggregation inhibitors in terms of oligomer and fibril formation. Based on their effects, the small molecules segregated into three distinct classes: compounds that inhibit oligomerization but not fibrillization, compounds that inhibit fibrillization but not oligomerization, and compounds that inhibit both. Several compounds selectively inhibited oligomerization at substoichiometric concentrations relative to amyloid beta monomer, with some active in the low nanomolar range. These results indicate that oligomers are not an obligate intermediate in the fibril formation pathway. In addition, these data suggest that small molecule inhibitors are useful for clarifying the mechanisms underlying protein aggregation and may represent potential therapeutic agents that target fundamental disease mechanisms.

Topics: Alzheimer Disease; Amyloid; Amyloid beta-Peptides; Animals; Humans; Plaque, Amyloid; Protein Structure, Quaternary; Thermodynamics

Cerebral amyloid beta-protein (Abeta) angiopathy (CAA) is a common pathological feature of Alzheimer's disease and several related disorders. In this condition, the accumulation offibrillar Abeta deposits is associated with degeneration of smooth muscle cells within the cerebral blood vessel wall. We have been using primary cultures of human cerebrovascular smooth muscle (HCSM) cells to investigate pathogenic mechanisms of Abeta in CAA. The specific assembly of Abeta fibrils on the surface of these cell types initiates several pathologic responses including increased expression and cell surface accumulation of the Abeta precursor protein (AbetaPP) and induction of apoptotic cell death. These pathologic responses are not observed with preparations of Abeta that are assembled into fibrils in solution, further underscoring the significance of the fibril assembly process on the cell surface. Since cell surface Abeta fibril assembly is the key initiator of the cerebrovascular cellular pathology that is observed in vitro, inhibition of this process remains an attractive therapeutic target for CAA. We have tested the efficacy of a variety of compounds that have been reported to inhibit Abeta fibril assembly in solution and block the neurotoxic properties of Abeta in vitro. The vast majority of these agents were ineffective in inhibiting the cell surface fibrillar assembly of Abeta and the subsequent pathologic responses in the cultured HCSM cells. This emphasizes the likely requirement of therapeutic compounds that are effective in disrupting cell surface-driven Abeta fibril assembly in the treatment of CAA.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Brain; Cell Membrane; Cells, Cultured; Cerebral Amyloid Angiopathy; Humans; Inositol; Macromolecular Substances; Melatonin; Microscopy, Electron; Muscle, Smooth, Vascular; Rifampin; Rolitetracycline

One of the major pathological features of Alzheimer's disease is the deposition of beta-amyloid peptide (Abeta). Cellular toxicity has been shown to be associated with fibrillar forms of Abeta; preventing this fibril formation is therefore viewed as a possible method of slowing disease progression in Alzheimer's disease. With the use of a series of tetracyclic and carbazole-type compounds as inhibitors of Abeta fibril formation, we here describe a number of common structural features that seem to be associated with the inhibitory properties of these agents. Compounds such as carvedilol, rolitetracycline and daunomycin, which are shown to inhibit Abeta fibril formation, also prevent the formation of species of peptide that demonstrate biological activity in a human neuroblastoma cell line. Molecular modelling data suggest that these compounds have in common the ability to adopt a specific three-dimensional pharmacophore conformation that might be essential for binding to Abeta and preventing it from forming fibrils. Understanding such drug-peptide interactions might aid the development of disease-modifying agents.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Carbazoles; Carvedilol; Cell Survival; Daunorubicin; Humans; Inhibitory Concentration 50; Microscopy, Electron; Models, Chemical; Molecular Structure; Neurons; Polymers; Propanolamines; Protein Binding; Rolitetracycline; Structure-Activity Relationship; Tetrazolium Salts; Thermodynamics; Thiazoles; Tumor Cells, Cultured