Effect of the six-mer synthetic peptide (AT1002) fragment of zonula occludens toxin on the intestinal absorption of cyclosporin A

Zonula occludens toxin (Zot) and its biologically active fragment, delta G, have been shown to reversibly open tight junctions (TJ) in endothelial and epithelial cells. Recently, a six-mer synthetic peptide H-FCIGRL-OH (AT1002) was identified and synthesized that retains the Zot permeating effect on intercellular TJ. The objective of this study was to evaluate the biological activity of AT1002 on enhancing the oral administration of cyclosporin A (CsA). The intestinal permeability enhancing effect of AT1002 on the transport of CsA across Caco-2 cell monolayers was examined after the following treatments, i.e., CsA, CsA/protease inhibitors (PI), CsA/PI/benzalkonium chloride (BC), CsA/AT1002, CsA/PI/AT1002, and CsA/PI/BC/AT1002 (CsA 0.5 μCi/ml, PI (bestatin 15 mM and E-64 5 mM), BC 0.005 w/v%, and AT1002 5 mM, respectively). Apparent permeability coefficients (Papp) were calculated for each treatment. In addition, four treatments, i.e., CsA, CsA/PI/BC, CsA/AT1002, and CsA/PI/BC/AT1002 (CsA 120 μCi/kg, PI (bestatin 30 mg/kg and E-64 10 mg/kg), BC 0.1 w/v%, and AT1002 doses of 5, 10 or 40 mg/kg, respectively) were prepared and administered intraduodenally to male Sprague–Dawley rats (230–280 g, n = 4–5). Blood samples were collected at 0, 20, 60, and 120 min post-dosing and CsA plasma concentrations were determined subsequently using a Beckman Liquid Scintillation Counter. No significant increases in CsA transport were observed in the Caco-2 cell culture experiments following pre-treatment with AT1002 (5 mM). Even though, AT1002 appeared to increase the Papp of CsA in each treatment (CsA/AT1002, 1.54 ± 0.13 × 10−6 cm/s and CsA/PI/AT1002, 1.76 ± 0.05 × 10−6 cm/s) compared to each control (CsA and CsA/PI), respectively. The plasma concentration of CsA was significantly increased over a range of 1.55–2.50 at 10 and 40 mg/kg dose of AT1002. Also, AUC0–120 min of CsA over a range of 1.64–2.14 and the Cmax of CsA over a range of 1.77–2.56 was statistically and significantly increased at 10 and 40 mg/kg of AT1002 after the intraduodenal administration of CsA/PI/BC/AT1002 to Sprague–Dawley rats. AT1002 significantly increased the in vivo oral absorption of CsA in the presence of PI. This study suggests that AT1002-mediated tight junction modulation, combined with metabolic protection and stabilization, may be used to enhance the low oral bioavailability of certain drugs when administered concurrently.