TR146 cells grown on filters as a model of human buccal epithelium: V. Enzyme activity of the TR146 cell culture model, human buccal epithelium and porcine buccal epithelium, and permeability of leu-enkephalin
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Abstract
The objective of the present study was to characterise the TR146 cell culture model
as an in vitro model of human buccal mucosa with respect to the enzyme activity in
the tissues. For this purpose, the contents of aminopeptidase, carboxypeptidase and
esterase in homogenate supernatants of the TR146 cell culture model, and human and
porcine buccal epithelium were compared. The esterase activity in the intact cell
culture model and in the porcine buccal mucosa was compared. Further, the TR146 cell
culture model was used to study the permeability rate and metabolism of leu-enkephalin.
The activity of the three enzymes in the TR146 homogenate supernatants was in the
same range as the activity in homogenate supernatants of human buccal epithelium.
In the TR146 cell culture model, the activity of aminopeptidase (13.70+/-2.10 nmol/min
per mg protein) was approx. four times the activity of carboxypeptidase (3.73+/-0.53
nmol/min per mg protein), whereas the level of esterase activity was significantly
higher (223.39+/-69.82 nmol/min per mg protein). In the TR146 cell culture model,
the apical esterase activity was found significantly higher than the basal activity,
and found comparable to the porcine buccal mucosa. However, the esterase activity
on the serosal side of the porcine buccal mucosa was higher than in the TR146 cell
culture model. Approx. 1.5% of leu-enkephalin permeated the TR146 cell layers within
5 h (P(app) 7.38+/-0.83x10(-7) cm/s) and approx. 77% of intact peptide was still present
in the donor phase after 5 h. The present study suggests that the TR146 cell culture
model is a valuable in vitro model for permeability and metabolism studies with enzymatically
labile drugs, such as leu-enkephalin, intended for buccal drug delivery.