Transport of the synthetic opioid peptide DADLE ([d-Ala2,d-Leu5]-Enkephalin) in neuronal cells

Sudha Ananth, Santoshanand V. Thakkar, Jaya P. Gnana-prakasam, Pamela M. Martin, Preethi S. Ganapathy, Sylvia B. Smith, Vadivel Ganapathy

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The sodium-coupled oligopeptide transporters 1 and 2 (SOPT1 and SOPT2) transport peptides consisting of at least five amino acids and show potential for the delivery of therapeutically relevant peptides/peptidomimetics. Here, we examined the expression of these two transporters in the retinal neuronal cell line RGC-5. These cells showed robust uptake activity for the synthetic pentapeptide DADLE ([d-Ala2,d-Leu5]-Enkephalin). The uptake was Na+ dependent and saturable (Kt, 6.2± 0.6μM). A variety of oligopeptides inhibited DADLE uptake. The uptake of the competing oligopeptides was directly demonstrated with fluorescein isothiocyanate-labeled Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys in RGC-5 cells and primary mouse retinal ganglion cells. The characteristics of DADLE uptake matched those of SOPT2. We then examined the expression of SOPT1 in these cells with deltorphin II (Tyr-d-Ala-Phe-Glu-Val-Val-Gly-NH2) as the substrate and found that RGC-5 cells also expressed SOPT1. As it is already known that SOPT1 is expressed in the neuronal cell line SK-N-SH, we investigated SOPT2 expression in these cells to determine whether the presence of both oligopeptide transporters is a common feature of neuronal cells. These studies showed that SK-N-SH cells also expressed SOPT2. This constitutes the first report on the functional characterization of SOPT1 and SOPT2 in retinal neuronal cells and on the expression of SOPT2 in nonretinal neuronal cells.

Original languageEnglish (US)
Pages (from-to)154-163
Number of pages10
JournalJournal of Pharmaceutical Sciences
Issue number1
StatePublished - Jan 2012


  • Active transport
  • Cell-penetrating peptides
  • Drug transport
  • Neuronal cells
  • Opioid peptides
  • Peptide delivery
  • Peptide transporters
  • Retinal ganglion cell

ASJC Scopus subject areas

  • Pharmaceutical Science


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