Action of neomycin on the metabolism of polyphosphoinositides in the guinea pig kidney

Mechanism of neomycin stimulation of D-glucose uptake in rabbit intestinal brush border membrane

In order to study the effect of the antibiotic neomycin on the intestinal epithelium, D-glucose was used as a probe molecule and its transport into rabbit brush border membrane vesicles was measured by a rapid filtration method. Treatment of the epithelium with neomycin sulfate prior to the preparation of the brush border membrane enhanced the D-glucose uptake, whereas neutral N-acetylated neomycin did not. This action of neomycin was related to its polycationic character and not to its bactericidal action. No significant difference could be demonstrated between the protein content or disaccharidase-specific activities of the brush border fractions from treated or non-treated intestines. Electrophoretic protein patterns of SDS-solubilized membrane were not significantly different after neomycin treatment. To gain more information on the mechanism involved in the stimulation of D-glucose transport, experiments were conducted on phosphatidyl glycerol artificial membranes and the results compared with those obtained with brush border membrane. At a concentration of 10(-7) M, neomycin decreased the nonactin-induced K+ conductance by a factor of approx. 100. The membrane conductance was linearly dependent on the neomycin concentration and the conductance in 10(-2) M KCl was 10 times that in 10(-3) M KCl. The valence of neomycin was estimated, from the slope of these curves, to be between 6 and 4. In contrast, acetylated neomycin had no effect on the nonactin-induced K+ membrane conductance. Therefore, the effect of neomycin on artificial membrane is related to its 4 to 6 positive charges. It is proposed that the stimulation of sugar transport in brush border membrane is related to screening of the membrane negative charges by the positively-charged neomycin. Accumulation of anions at the membrane surface then occurs and their diffusion into the intravesicular space would increase the transmembrane potential which, in turn, stimulates the entry of D-glucose.

A biochemical mechanism of the ototoxic interaction between neomycin and ethacrynic acid

The effects of neomycin on tissue levels of ethacrynic acid was studied in vivo and in vitro. In vitro, the addition of neomycin to incubations of synaptosomes and inner ear tissues of guinea pigs raised the concentration of bound ethacrynate approximately two-fold. In vivo, radioactive ethacrynate was determined in the inner ear of mice by radioautography after intravenous injection of the drug (50 mg/kg body weight). Treatment of animals with neomycin (100 mg/kg body weight, intramuscularly) 60 min prior to ethacrynate led to a three-to five-fold higher accumulation of ethacrynate in cochlear structures. It is suggested that neomycin breaks down hemolabyrinthine or tissue permeability barriers and allows increased penetration of the other drug into the inner ear.

Interactions of neomycin with monomolecular films of polyphosphoinositides and other lipids

The interactions of calcium and the aminoglycosidic antibiotic, neomycin, with various lipids were investigated in monomolecular films. Lipids were spread over a subphase of 0.05 M N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, pH 7.0, and NaCl to give an ionic strength of 0.2. Measurements of surface pressure (pi) were taken with a Wilhelmy balance. In the absence of Ca2+, 1 muM--1 mM neomycin in the subphase decreased pi (i.e. condensed films) of all acidic lipids tested. In the presence of 1 mM Ca2+, neomycin did not change pi of films of phosphatidylserine, phosphatidylinositol and phosphatidic acid while it lowered pi of cardiolipin and cerebroside sulfate films. A unique pattern of interaction was observed with polyphosphoinositide monolayers. In the absence of Ca2+, 1 muM neomycin decreased pi followed by an increase of pi at higher neomycin concentrations. Ca2+ (1 mM) condensed the film significantly more than did neomycin. However, as little as 1 muM neomycin induced expansion of the calcium/lipid film which at 1 mM neomycin reached the same pi as in the absence of Ca2+. Such expansion was observed at all pressures of the film including the collapse pressure indicating a strong 'complex' between the drug and polyphosphoinositide not antagonized by Ca2+. In the absence of possible hydrophobic interactions, both the condensation and the expansion of the film should be mediated by ionic forces. Combined in vivo and in vitro evidence is discussed to suggest the polyphosphoinositides as the physiological receptors for aminoglycosides in the mammalian cell membrane.

Isolation of an aminoglycoside receptor from guinea pig inner ear tissues and kidney

Affinity chromatography was used to isolate aminoglycoside receptors from inner ear tissues and kidney. Neomycin was immobilized on glass beads and served as the stationary phase in column chromatography. Fractionation of an organic tissue extract on this matrix demonstrated two components with high affinity for neomycin: phohphatidyl inositol phosphate and phosphatidyl inositol diphosphate. The toxicity of aminoglycosides is explained on the basis of a drug-interaction with these lipids.