gramicidin-a and Disease-Models--Animal

We sought to develop a therapeutic agent that would permit prolongation of survival in rats subjected to lethal hemorrhagic shock (HS), even in the absence of resuscitation with asanguinous fluids or blood.. We synthesized a series of compounds that consist of the electron scavenger and superoxide dismutase mimic, 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl (4-NH2-TEMPO), conjugated to fragments and analogs of the membrane-active cyclopeptide antibiotic, gramicidin S. Using an in vivo assay, wherein isolated intestinal segments were loaded inside the lumen with various test compounds, we studied these compounds for their ability to prevent ileal mucosal barrier dysfunction induced by subjecting rats to profound HS for 2 hours. The most active compound in this assay, XJB-5-131, ameliorated peroxidation of the mitochondrial phospholipid, cardiolipin, in ileal mucosal samples from rats subjected to HS. XJB-5-131 also ameliorated HS-induced activation of the pro-apoptotic enzymes, caspases 3 and 7, in ileal mucosa. Intravenous treatment with XJB-5-131 (2 micromol/kg) significantly prolonged the survival of rats subjected to profound blood loss (33.5 mL/kg) despite administration of only a minimal volume of crystalloid solution (2.8 mL/kg) and the absence of blood transfusion.. These data support the view that mitochondrially targeted electron acceptors and SOD mimics are potentially valuable therapeutics for the treatment of serious acute conditions, such as HS, which are associated with marked tissue ischemia.

Topics: Animals; Anti-Bacterial Agents; Cells, Cultured; Cyclic N-Oxides; Disease Models, Animal; Drug Therapy, Combination; Follow-Up Studies; Gramicidin; Intestinal Mucosa; Lipid Peroxidation; Male; Mitochondria; Permeability; Rats; Rats, Sprague-Dawley; Shock, Hemorrhagic; Spin Labels; Superoxide Dismutase; Survival Rate; Treatment Outcome

Transient cerebral ischemia kills CA1 pyramidal cells of the hippocampus, whereas most CA1 interneurons survive. It has been proposed that calcium-binding proteins, neurotrophins, and/or inhibitory neuropeptides protect interneurons from ischemia. However, different synaptic responses early after reperfusion could also underlie the relative vulnerabilities to ischemia of pyramidal cells and interneurons. In this study, we used gramicidin perforated patch recording in ex vivo slices to investigate gamma-aminobutyric acid (GABA) synaptic function in CA1 pyramidal cells and interneurons 4 h after a bilateral carotid occlusion accompanied by hypovolemic hypotension. At this survival time, the amplitudes of both miniature inhibitory postsynaptic currents (mIPSCs) and GABA-evoked currents were reduced in CA1 pyramidal cells, but not in CA1 interneurons. In addition, the mean rise time of mIPSCs was reduced in pyramidal cells. The reversal potential for the GABA current (E(GABA)) did not shift toward depolarizing values in either cell type, indicating that the driving force for chloride was unchanged at this survival time. We conclude that early during reperfusion GABAergic neurotransmission is attenuated exclusively in pyramidal neurons. This is likely explained by reduced GABAA receptor sensitivity or clustering and possibly also reduced GABA release, rather than by an elevation of intracellular chloride. Impaired GABA function may contribute to ischemic neuronal death by enhancing the excitability of CA1 pyramidal cells and facilitating N-methyl-D-aspartic acid channel opening. Therefore, normalizing GABAergic function might be a useful pharmacological approach to counter excessive, and potentially excitotoxic, glutamatergic activity during the postischemic period.

Topics: Animals; Disease Models, Animal; gamma-Aminobutyric Acid; Gramicidin; Hippocampus; Interneurons; Ischemic Attack, Transient; Male; Models, Neurological; Prosencephalon; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Reperfusion; Sensitivity and Specificity; Synapses; Synaptic Transmission; Tissue Culture Techniques

Gramicidin S (GrS) suppressed the onset of experimental autoimmune uveoretinitis (EAU) induced with S-antigen in rats, and the proliferation of mitogen-stimulated lymphocytes in culture. As an immunosuppressive mechanism of the cyclic peptide antibiotic we first postulated that the drug exerts its effect as an ionophore. Although all ionophore compounds tested suppressed lymphocyte proliferation, no correlation was observed between changes in intracellular concentrations of Na+ and K+ and the degree of immunosuppression. For example, monensin inhibited lymphocyte proliferation without affecting intracellular Na+ and K+ levels. Thus it was likely that the immunosuppressive effects of the ionophore compounds including GrS were due to their ability to modify cell membrane properties rather than their ionophore activity. We then tested the hypothesis that GrS inhibits transport of metabolic intermediates or metabolites (thymidine and methionine) into lymphocytes. The idea was experimentally supported. Further, inhibition of metabolite transport by GrS was found to be reversible. To investigate whether inhibition of metabolite uptake can be a mechanism of immunosuppression of EAU, endogenously stimulated lymphocytes were isolated from S-antigen-immunized rats at different stages of EAU and the effect of GrS on metabolite uptake by the cells was determined. The activity of lymphocytes to transport metabolites was enhanced at pre-EAU stages and the enhanced metabolite uptake was markedly inhibited by GrS. We interpreted the result to support that inhibition of metabolite uptake by GrS is probably a mechanism of immunosuppression in vivo by this drug.

Topics: Animals; Antigens; Arrestin; Autoimmune Diseases; Biological Transport; Cells, Cultured; Disease Models, Animal; Eye Proteins; Female; Gramicidin; Immunosuppressive Agents; Ionophores; Lymphocyte Activation; Lymphocytes; Methionine; Potassium; Rats; Rats, Inbred Lew; Sodium; Thymidine; Uveitis, Posterior

Topics: Animals; Anterior Chamber; Atropine; Cornea; Disease Models, Animal; Gramicidin; Inflammation; Male; Methods; Neomycin; Nylons; Phenylephrine; Polymyxins; Postoperative Care; Postoperative Complications; Rabbits; Suture Techniques; Sutures; Textiles; Wound Healing

Topics: Administration, Topical; Animals; Atropine; Cornea; Corneal Injuries; Dexamethasone; Disease Models, Animal; Gramicidin; Male; Neomycin; Parasympatholytics; Phenylephrine; Polymyxins; Rabbits; Wound Healing