A. Bernkop-schnurch et al., Thiolated polymers: synthesis and in vitro evaluation of polymer-cysteamine conjugates, INT J PHARM, 226(1-2), 2001, pp. 185-194
The purpose of the present study was to synthesize and characterize novel t
hiolated polymers. Mediated by a carbodiimide cysteamine was covalently lin
ked to sodium carboxymethylcellulose (CMC) and polycarbophil (PCP). The res
ulting CMC-cysteamine conjugates displayed 77.9 +/- 6.7 and 365.1 +/- 8.7 p
mol thiol groups per gram of polymer, whereas the PCP-cysteamine conjugates
showed 26.3 +/- 1.9 and 122.7 +/- 3.8 mu mol thiol groups per gram of poly
mer (mean +/- S.D.; n = 3). In aqueous solutions above pH 5.0 both modified
polymers were capable of forming inter- and/or intra-molecular disulfide b
onds. The reaction velocity of this oxidation process was accelerated with
a decrease in the proton concentration. The oxidation proceeded more rapidl
y within thiolated CMC than within thiolated PCP. Permeation studies carrie
d out in Ussing-type chambers with freshly excised intestinal mucosa from g
uinea pigs utilizing sodium fluorescein as model drug for the paracellular
uptake revealed an enhancement ratio (R = P-app (conjugate)/P-app (control)
) of 1.15 and 1.41 (mean +/- S.D.; n = 3) for the higher thiolated CMC-cyst
eamine (0.5%; m/v) and PCP-cysteamine conjugate (1.0%; m/v), respectively.
The decrease in the transepithelial electrical resistance values was in goo
d correlation with the enhancement ratios. Due to a high crosslinking tende
ncy by the formation of disulfide bonds stabilizing drug carrier systems ba
sed on thiolated polymers and a permeation enhancing effect, CMC- and PCP-c
ysteamine conjugates represent promising excipients for the development of
novel drug delivery systems. (C) 2001 Published by Elsevier Science B.V.