Inactivation and aggregation of b-galactosidase in lyophilized formulation described by Kohlraushu-Williams-Watts Streched exponential function
The
purpose of study was to examine whether the empirical Kohlrausch-Williams-Watts
(KWW) equation is applicable to not only protein aggregation but also protein
denaturation in lyophilized formulations. Lyophilized b-galactosidase
(b-GA)
formulations containing polyvinylalcohol and methylcellulose were used as model
formulations. The possibility of
predicting storage stability based on the temperature dependence of the
estimated parameters of inactivation/aggregation time constant (t)
and its distribution (b)
was discussed. Inactivation and
aggregation of b-GA
were describable with the empirical KWW equation, regardless of whether the
temperature was above or below the NMR relaxation-based critical mobility
temperature (Tmc), or whether protein molecules with different
degrees of deformation resulting from stresses during lyophilization exist in
the formulation. The estimated b
parameter for protein aggregation decreased rapidly as temperature increased
beyond Tmc because the mobility of polymer molecules increased in the
initial stages of glass transition. The
time required for 10% enzyme to aggregate (t90) calculated from the t
and b
parameters exhibited a change in temperature dependence gradient near Tmc.
In contrast, t90 for
protein inactivation exhibited temperature dependence patterns varying with the
excipients. The t90 calculated from the estimated t
and b
parameters was found to be a useful parameter for evaluating the stability of
lyophilized b-GA
formulations. The prediction of t90
by extrapolation was possible in the temperature range in which b
did not rapidly vary with temperature.