Different internalization pathways of polymeric micelles and unimers and their effects on vesicular transport

Efficient entry of synthetic polymers inside cells is a central issue in polymeric drug delivery. Though polymers are widely believed to interact nonspecifically with plasma membrane, we present unexpected evidence that amphiphilic block copolymers, depending on their aggregation state, can distinguish between caveolae- and clathrin-mediated endocytosis. A block copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), Pluronic P85 (P85), below critical micelle concentration (CMC) exists as single molecule coils (unimers) and above CMC forms 14.6 nm aggregated micelles with a hydrophobic PPO core and hydrophilic PEO shell. The internalization pathways of P85 in mammalian cells were elucidated using endocytosis inhibitors and colocalization with endocytosis markers (clathrin-specific antibodies and transferrin for clathrin and caveolin-1-specific antibodies and cholera toxin B for caveolae). Altogether, our results indicate that P85 unimers internalize through caveolae-mediated endocytosis, while P85 micelles internalize through clathrin-mediated endocytosis. Furthermore, at concentrations above 0.01% P85 inhibits caveolae-mediated endocytosis (cholera toxin B), while having little or no effect on the clathrin-mediated endocytosis (transferrin). Selective interaction of Pluronic with caveolae may explain its striking pharmacological activities including inhibition of drug efflux transport, activation of gene expression, and dose-dependent hyperlipidemia.     

The effect of a temporal shift in diurnal geomagnetic variation on roach Rutilus rutilus L. embryos: A comparison with effects of simulated geomagnetic storms

A study was made of the effects that 6- and 12-h shifts in diurnal geomagnetic variation relative to the night–day light cycles exert on roach Ritulus ritulus L. embryos. Either temporal shift in diurnal geomagnetic variation stimulated blastomere proliferation and early prelarval hatching in exposed embryos compared to controls. Underyearlings developing from exposed embryos displayed higher locomotor activity in a plusshaped maze, a lower number of rays in the anal fin, a redistribution of vertebrae through sections of the vertebral column, and a higher number of seismosensory system openings in the mandibular and preopercular bones. The effects were similar to those described previously for roaches exposed to a simulated geomagnetic storm during embryonic development. The results support the hypothesis that animals perceive geomagnetic storms as a dramatic disturbance that occurs in the habitual diurnal geomagnetic variation at an unusual time relative to the night–day light cycle, which acts as a primary zeitgeber of circadian biological rhythms.

     

Increasing cytostatic effects of ricin A chain and Staphylococcus aureus enterotoxin A through in vitro hydrophobization with fatty acid residues

In order to impart an ability for receptor-independent transmembrane transfer to water-soluble proteins, it has been suggested that they be hydrophobized by lipid groups (fatty acids, etc.). To this end, systems of reversed micelles of surfactants in organic solvents were used as reaction media for protein modification. It was shown that after introduction of a hydrophobic anchor (stearic acid residue) the toxic effect of ricin A-chain (in the absence of B-chain) on intact cells became very close to that of the native toxin. As a result of stearic acid acylation, the activity of Staphylococcal enterotoxin A increased by nearly 1.5-2 orders. The observed phenomena can be explained by receptor-independent intracellular translocation of the hydrophobized toxins.