Several polycations possessing substantial buffering capacity below physiological pH, such as lipopolyamines and polyamidoamine polymers, are efficient transfection agents per se-i.e., without the addition of cell targeting or membrane-disruption agents. This observation led us to test the cationic polymer polyethylenimine (PEI) for its genedelivery potential. Indeed, every third atom of PEI is a protonable amino nitrogen atom, which makes the polymeric network an effective "proton sponge" at virtually any pH. Luciferase reporter gene transfer with this polycation into a variety of cell lines and primary cells gave results comparable to, or even better than, lipopolyamines. Cytotoxicity was low and seen only at concentrations well above those required for optimal transfection. Delivery of oligonucleotides into embryonic neurons was followed by using a fluorescent probe.Virtually all neurons showed nuclear labeling, with no toxic effects. The optimal PEI cation/anion balance for in vitro transfection is only slightly on the cationic side, which is advantageous for in vivo delivery. Indeed, intracerebral luciferase gene transfer into newborn mice gave results comparable (for a given amount of DNA) to the in vitro transfection of primary rat brain endothelial cells or chicken embryonic neurons. Together, these properties make PEI a promising vector for gene therapy and an outstanding core for the design of more sophisticated devices. Our hypothesis is that its efficiency relies on extensive lysosome buffering that protects DNA from nuclease degradation, and consequent lysosomal swelling and rupture that provide an escape mechanism for the PEI/DNA particles. Nonviral gene-delivery techniques remain several orders of magnitude behind viral vectors when compared on the basis of the mean number of gene copies needed to transfect a cell. Despite this limitation, plasmid-mediated transfection has the major advantage that it raises none of the concerns of biological vectors for human therapy. Thus, much effort is presently devoted to improving nonviral techniques (1). Indeed, the advent of gene therapy has provided the impetus for improving, by appropriate chemical design, the efficiency of classical transfection agents such as cationic polymers (DEAE-dextran, Polybrene, polylysine) or inorganic aggregates (e.g., calcium phosphate). Various other polycationic cores have been developed, whether macromolecules (for review, see refs. 2-4), amphiphilic aggregates (for review, see ref. 5), or mixtures of both (6, 7), all of which ionically condense plasmid DNA and bind to the cell surface. Additional viral-like molecular properties have been added to these particles (2-9) to promote receptor-mediated endocytosis, fusogenicity, and karyophily. Among the cationic cores described so far, two are constitutively efficient gene-delivery agents without any extra virusderived function or lysosomotropic additive. Polyamidoamine cascade polymers (4) and lipopolyamines (5, 10-12), although quite different in chemical structures, ...

[Abstract unavailable

Oxidative stress-induced neuronal cell death has been implicated in different neurological disorders and neurodegenerative diseases; one such ailment is Alzheimer's disease. Using the Alzheimer's disease-associated amyloid beta protein, glutamate, hydrogen peroxide, and buthionine sulfoximine, we investigated the neuroprotective potential of estrogen against oxidative stress-induced cell death. We show that 17-beta-estradiol, its nonestrogenic stereoisomer, 17-alpha-estradiol, and some estradiol derivatives can prevent intracellular peroxide accumulation and, ultimately, the degeneration of primary neurons, clonal hippocampal cells, and cells in organotypic hippocampal slices. The neuroprotective antioxidant activity of estrogens is dependent on the presence of the hydroxyl group in the C3 position on the A ring of the steroid molecule but is independent of an activation of estrogen receptors.