Gm. Pauletti et al., EFFECT OF SIZE AND CHARGE ON THE PASSIVE DIFFUSION OF PEPTIDES ACROSSCACO-2 CELL MONOLAYERS VIA THE PARACELLULAR PATHWAY, Pharmaceutical research, 14(2), 1997, pp. 164-168
Purpose. To evaluate the effect of size and charge on the permeation c
haracteristics of peptides across the intestinal mucosa. Methods. The
lipophilicities of neutral, positively and negatively charged capped a
mino acids (Asn, Lys, Asp), tripeptides (Ac-Gly-X-Ala-NH2; X = Asn, Ly
s, Asp) and hexapeptides (Ac-Trp-Aia-Gly-Gly-X-Ala-NH2; X = Asn, Lys,
Asp) were estimated using an immobilized artificial membrane. The diff
usion coefficients used to calculate the molecular radii were measured
by NMR. The transport characteristics of the model peptides were dete
rmined across Caco-2 cell monolayers. Results, When model compounds ha
ving the same charge were compared, permeation was highly size-depende
nt (capped amino acids > tripeptides > hexapeptides), suggesting trans
port predominantly via the paracellular route. For example, the flux o
f the negatively charged Asp amino acid (P-app = 10.04 +/- 0,43 x 10(-
8) cm/s) was 3 times greater than that observed for the Asp-containing
hexapeptide (P-app = 3.19 +/- 0.27 x 10(-8) cm/s). When model compoun
ds of the same size were compared, permeation across the cell monolaye
r was charge-dependent (negative < positive less than or equal to neut
ral). For example, the neutral, Asn-containing tripeptide (P-app = 25.
79 +/- 4.86 x 10(-8) cm/s) was substantially more able to permeate the
Caco-2 cell monolayer than the negatively charged Asp-containing trip
eptide (P-app = 7.95 +/- 1.03 x 10(-8) cm/s) and the positively charge
d Lys-containing tripeptide (P-app = 9.86 +/- 0.18 x 10(-8) cm/s). The
permeability of the cell monolayer to peptides became less sensitive
to net charge as the size of the peptides increased. Conclusions. A po
sitive net charge of hydrophilic peptides enhances their permeation ac
ross the intestinal mucosa via the paracellular pathway. With increasi
ng molecular size, molecular sieving of the epithelial barrier dominat
es the transport of peptides, and the effect of the net charge becomes
less significant.