Cp. Pujara et al., EFFECTS OF FORMULATION VARIABLES ON NASAL EPITHELIAL-CELL INTEGRITY -BIOCHEMICAL EVALUATIONS, International journal of pharmaceutics, 114(2), 1995, pp. 197-203
The effects of pH, osmolarity, type and concentration of buffers on th
e nasal mucosal epithelium have been investigated in rats using an in
situ nasal perfusion technique. Traditionally, histological approaches
which are qualitative and not predicitive of nasal mucosal sensitivit
y, have been used to assess the damage to the nasal mucosa. A biochemi
cal approach has been used in this report to assess irritation to the
nasal mucosa which may provide a priori indication of nasal sensitivit
y to chronic use of nasal formulations. The nasal mucosal irritation m
ay be predicted by determining the amount of total protein and two enz
ymes, lactate dehydrogenase (LDH, EC 1.1.1.27), a cytosolic enzyme and
5'-nucleotidase (5'-ND, EC 3.1.3.5), a membrane-bound enzyme released
during perfusion. To determine the effect of pH on the nasal mucosa,
phosphate buffers ranging in pH from 2 to 12 were utilized. solutions
within a pH range of 3-10 caused minimal release of the biochemical ma
rkers whereas solutions of pH above 10 caused significant membrane and
intracellular enzyme release. Acetate buffers (pH 4.75) at three diff
erent concentrations, 0.07, 0.14 and 0.21 M, were used to study the ef
fect of buffer concentration on the nasal mucosal integrity. The resul
ts indicate that the alteration to the nasal mucosal cells by buffers
is concentration dependent. To study the effect of buffer type, four d
ifferent buffers, i.e., acetate, adipate, citrate, and phosphate (0.07
M, pH 4.75) were studied. The acetate buffer was found to have the mo
st irritation potential when compared to adipate, citrate, and phospha
te buffers. To determine the effects of unionized and ionized species
of a buffer, 0.025 M benzoate buffers at pH 3.2 and 5.2 were studied.
The results indicate that the unionized species of benzoic acid causes
more cellular perturbation than the ionized species. Hypertonic and i
sotonic sodium chloride solutions caused minimal mucosal cell aberrati
ons while hypotonic solutions caused extensive leakage of LDH. These r
esults along with other results from our laboratory may help in design
ing well tolerated nasal formulations for chronic use.