Lens
is the avascular tissue in the eye between the aqueous humor
and vitreous. Drug binding to the lens might affect ocular pharmacokinetics,
and the binding may also have a pharmacological role in drug-induced
cataract and cataract treatment. Drug distribution in the lens has
been studied in vitro with many compounds; however, the experimental
methods vary, no detailed information on distribution between the
lens sublayers exist, and the partition coefficients are reported
rarely. Therefore, our objectives were to clarify drug localization
in the lens layers and establish partition coefficients for a wide
range of molecules. Furthermore, we aimed to illustrate the effect
of lenticular drug binding on overall ocular drug pharmacokinetics.
We studied the distribution of 16 drugs and three fluorescent dyes
in whole porcine lenses in vitro with imaging mass spectrometry and
fluorescence microscopy techniques. Furthermore, we determined lens/buffer
partition coefficients with the same experimental setup for 28 drugs
with mass spectrometry. Finally, the effect of lenticular binding
of drugs on aqueous humor drug exposure was explored with pharmacokinetic
simulations. After 4 h, the drugs and the dyes distributed only to
the outermost lens layers (capsule and cortex). The lens/buffer partition
coefficients for the drugs were low, ranging from 0.05 to 0.8. On
the basis of the pharmacokinetic simulations, a high lens-aqueous
humor partition coefficient increases drug exposure in the lens but
does not significantly alter the pharmacokinetics in the aqueous humor.
To conclude, the lens seems to act mainly as a physical barrier for
drug distribution in the eye, and drug binding to the lens affects
mainly the drug pharmacokinetics in the lens.