title: Injectable liposomal formulations of opiorphin as a new therapeutic strategy in pain management.
abstract: BACKGROUND
  Conventional and PEGylated liposomes were developed, aimed at improving the pain-killing effect of opiorphin.
  
  
  METHODS
  The antinociceptive action of the formulations was investigated on rats (tail-flick test), and compared with that of opiorphin and morphine aqueous solutions (all at 5 mg/kg).
  
  
  RESULTS
  Opiorphin loading in conventional liposomes enabled a 28% AUC increase with respect to free peptide. PEGylated liposomes provided AUC values 80, 60 and 40% higher than free peptide, morphine and opiorphin-loaded conventional liposomes, respectively. Moreover, opiorphin entrapment in PEGylated liposomes increased analgesic effect duration by more than 50%. These results were attributed to the greater effectiveness of PEGylated liposomes in protecting the drug and prolonging its circulation time.
  
  
  CONCLUSIONS
  Opiorphin-loaded PEGylated-liposomes can represent a valid alternative to morphine in pain management.
authors.affiliation: Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy; Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy.
authors.forename: Natascia
authors.initials: N
authors.lastname: Mennini
authors.affiliation: Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy; Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Mura
authors.affiliation: Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy; Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Nativi
authors.affiliation: Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy; Department of Chemistry, University of Florence, Polo Scientifico Sesto Fiorentino, Sesto Fiorentino (FI), Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Richichi
authors.affiliation: Department of Neurosciences, Psychology, Drug Research & Child Health, University of Florence, Firenze, Italy; Department of Neurosciences, Psychology, Drug Research & Child Health, University of Florence, Firenze, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Di Cesare Mannelli
authors.affiliation: Department of Neurosciences, Psychology, Drug Research & Child Health, University of Florence, Firenze, Italy; Department of Neurosciences, Psychology, Drug Research & Child Health, University of Florence, Firenze, Italy.
authors.forename: Carla
authors.initials: C
authors.lastname: Ghelardini
keywords: PEGylated liposomes; conventional liposomes; improved antinociception; opiorphin; tail-flick latency test