melitten and Sepsis

Melittin is one of the most studied antimicrobial peptides, and several in vitro experiments have demonstrated its antibacterial efficacy. However, there is evidence showing melittin has non-promising effects such as cytotoxicity and hemolysis. Therefore, concerns about unwanted collateral toxicity of melittin lie ahead in the path toward its clinical development. With these considerations, the present study aimed to fill the gap between in vitro and in vivo studies.. In the first step, in vitro toxicity profile of melittin was assessed using cytotoxicity and hemolysis tests. Next, a maximum intraperitoneal (i.p.) sub-lethal dose was determined using BALB/c mice. Besides toxicity, antimicrobial efficacy of melittin against extensively drug-resistant (XDR) Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus (MRSA), and KPC-producing Klebsiella pneumonia (KPC-KP) pathogens were tested using both in vitro and in vivo methods.. These results indicate that melittin at its safe dose could not exhibit antimicrobial activity, which hinders its application in clinical practice.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Animals; Anti-Bacterial Agents; Cell Line; Drug Resistance, Bacterial; Hemolysis; Humans; Klebsiella Infections; Klebsiella pneumoniae; Male; Melitten; Methicillin-Resistant Staphylococcus aureus; Mice, Inbred BALB C; Microbial Sensitivity Tests; Peritonitis; Sepsis; Staphylococcal Infections

Pan-resistant Acinetobacter baumannii have prompted the search for therapeutic alternatives. We evaluate the efficacy of four cecropin A-melittin hybrid peptides (CA-M) in vivo. Toxicity was determined in mouse erythrocytes and in mice (lethal dose parameters were LD(0), LD(50), LD(100)). Protective dose 50 (PD(50)) was determined by inoculating groups of ten mice with the minimal lethal dose of A. baumannii (BMLD) and treating with doses of each CA-M from 0.5 mg/kg to LD(0). The activity of CA-Ms against A. baumannii was assessed in a peritoneal sepsis model. Mice were sacrificed at 0 and 1, 3, 5, and 7-h post-treatment. Spleen and peritoneal fluid bacterial concentrations were measured. CA(1-8)M(1-18) was the less haemolytic on mouse erythrocytes. LD(0) (mg/kg) was 32 for CA(1-8)M(1-18), CA(1-7)M(2-9), and Oct-CA(1-7)M(2-9), and 16 for CA(1-7)M(5-9). PD(50) was not achieved with non-toxic doses (≤ LD(0)). In the sepsis model, all CA-Ms were bacteriostatic in spleen, and decreased bacterial concentration (p < 0.05) in peritoneal fluid, at 1-h post-treatment; at later times, bacterial regrowth was observed in peritoneal fluid. CA-Ms showed local short-term efficacy in the peritoneal sepsis model caused by pan-resistant Acinetobacter baumannii.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Ascitic Fluid; Drug Resistance, Bacterial; Erythrocytes; Female; Humans; Injections, Intraperitoneal; Lethal Dose 50; Melitten; Mice; Mice, Inbred C57BL; Microbial Sensitivity Tests; Models, Animal; Recombinant Fusion Proteins; Sepsis; Spleen; Time Factors

Contraction-induced respiratory muscle fatigue and sepsis-related reductions in respiratory muscle force-generating capacity are mediated, at least in part, by reactive oxygen species (ROS). The subcellular sources and mechanisms of generation of ROS in these conditions are incompletely understood. We postulated that the physiological changes associated with muscle contraction (i.e., increases in calcium and ADP concentration) stimulate mitochondrial generation of ROS by a phospholipase A(2) (PLA(2))-modulated process and that sepsis enhances muscle generation of ROS by upregulating PLA(2) activity. To test these hypotheses, we examined H(2)O(2) generation by diaphragm mitochondria isolated from saline-treated control and endotoxin-treated septic animals in the presence and absence of calcium and ADP; we also assessed the effect of PLA(2) inhibitors on H(2)O(2) formation. We found that 1) calcium and ADP stimulated H(2)O(2) formation by diaphragm mitochondria from both control and septic animals; 2) mitochondria from septic animals demonstrated substantially higher H(2)O(2) formation than mitochondria from control animals under basal, calcium-stimulated, and ADP-stimulated conditions; and 3) inhibitors of 14-kDa PLA(2) blocked the enhanced H(2)O(2) generation in all conditions. We also found that administration of arachidonic acid (the principal metabolic product of PLA(2) activation) increased mitochondrial H(2)O(2) formation by interacting with complex I of the electron transport chain. These data suggest that diaphragm mitochondrial ROS formation during contraction and sepsis may be critically dependent on PLA(2) activation.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Animals; Arachidonic Acid; Calcium; Cyanides; Diaphragm; Electron Transport Complex I; Electron Transport Complex IV; Enzyme Inhibitors; Hydrogen Peroxide; Malates; Male; Melitten; Mitochondria; NADH, NADPH Oxidoreductases; NADPH Oxidases; Onium Compounds; Phosphodiesterase Inhibitors; Phospholipases A; Pyruvic Acid; Rats; Rats, Inbred Strains; Reactive Oxygen Species; Rotenone; Sepsis; Terpenes; Uncoupling Agents