title: Liposomal formulations of inflammatory bowel disease drugs: local versus systemic drug delivery in a rat model.
abstract: OBJECTIVE
  Based on adherence to intestinal mucosa, intralumenally administered liposomal formulations of 5-aminosalicylate (5-ASA) and 6-mercaptopurine (6-MP) were studied for their potential to enhance local drug delivery to intestinal tissue for the treatment of inflammatory bowel disease.
  
  
  METHODS
  5-ASA was encapsulated in standard phospholipid liposomes while 6-MP required encapsulation in nonphospholipid liposomes to obtain equivalent drug loading. Encapsulation efficiency was measured by size-exclusion chromatography/high-performance liquid chromatogtaphy (HPLC). Liposomal formulations or solution of the drugs were injected into unligated jejunum to compare pharmacokinetics and into ligated loops of rat ileum and colon to evaluate local delivery. Dextran sulfate and acetic acid induced colitis were used as models of lower intestinal inflammation. Plasma, tissue and luminal drug and metabolite levels were measured by liquid scintillation counting or HPLC.
  
  
  RESULTS
  Encapsulation efficiency of 6-MP was dependent on lipid content and composition. While liposomal encapsulation significantly reduced systemic absorption of 5-ASA this was not the case for 6-MP. Liposomal adherence to intestinal tissue resulted in increased tissue levels for 5-ASA; however, 6-MP local tissue levels were not improved compared to solution drug.
  
  
  CONCLUSIONS
  Nonphospholipid liposomes optimize encapsulation of 6-MP. While liposomal formulations show potential for local drug delivery to diseased bowel, drug physicochemical properties, absorption, and metabolic profiles dictate tissue-targeting potential. Liposomes reduce systemic availability from paracellular absorption of hydrophilic 5-ASA, but fail to improve local tissue delivery of 6-MP, a molecule absorbed by passive membrane permeation that undergoes extensive first- pass metabolism.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, The University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
authors.forename: Filippos
authors.initials: F
authors.lastname: Kesisoglou
authors.forename: Simon Yuji
authors.initials: SY
authors.lastname: Zhou
authors.forename: Susan
authors.initials: S
authors.lastname: Niemiec
authors.forename: Jordan Wing
authors.initials: JW
authors.lastname: Lee
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Zimmermann
authors.forename: David
authors.initials: D
authors.lastname: Fleisher
mesh_terms: D000465:Algorithms; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000493:pharmacokinetics; D001693:Biological Transport, Active; D018938:Caco-2 Cells; D055598:Chemical Phenomena; D002626:Chemistry, Pharmaceutical; D002627:Chemistry, Physical; D003092:Colitis / Q000378:metabolism; D004337:Drug Carriers; D004339:Drug Compounding; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy*; D007408:Intestinal Absorption; D008081:Liposomes; D008297:Male; D015122:Mercaptopurine / Q000008:administration & dosage / Q000493:pharmacokinetics; D019804:Mesalamine / Q000008:administration & dosage / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D004337:Drug Carriers; D007166:Immunosuppressive Agents; D008081:Liposomes; D019804:Mesalamine; D015122:Mercaptopurine