Abstract
Purpose: :
Latanoprost is an isopropyl ester prostaglandin F2α analogue prodrug indicated for the treatment of open-angle glaucoma. Latanoprost is hydrolyzed in the eye to the biologically active metabolite, latanoprost acid. The objective of this study was to assess the extent of latanoprost hydrolysis in various human ocular tissues. Insight in the enzymatic activity of these tissues is useful for the interpretation of human data and the design and testing of new drugs for ophthalmology.
Methods: :
Whole human eyes were obtained from tissue banks within 24 hours post-mortem. The eyes were dissected into aqueous humor, cornea, conjunctiva, ciliary body, retina, choroid, and sclera. Each tissue was divided into two pieces, blotted, and weighed. The two replicates from individual tissues were then transferred to separate incubation tubes containing Glutathione-bicarbonated Ringer’s (GBR) buffer, pH 7.4. Latanoprost was dosed at a concentration of 20 μM, the tubes were incubated at 37°C, and samples were collected at the onset of the incubation and at pre-determined time points up to 4 hours. Disappearance of latanoprost and formation of the active metabolite latanoprost acid were analyzed using LC-MS/MS.
Results: :
Most of the dosed latanoprost disappeared within 2 hours of incubation with the various human ocular tissues, except aqueous humor. The apparent formation of latanoprost acid was slightly lower than the degradation of the parent compound at each time point (possibly due to non-specific binding of latanoprost to tissue), and accounted for approximately 40-90% of the dose at the end of the incubation. Across tissues, the rate of formation of latanoprost acid correlated well with the rate of degradation of the parent compound. When normalized for tissue weight, the rate of hydrolysis of latanoprost was highest in choroid > ciliary body ≈ cornea ≈ conjunctiva. These results are similar to data obtained with ocular tissues from pigmented rabbits under similar experimental conditions.
Conclusions: :
The results demonstrate that latanoprost is extensively hydrolyzed in a majority of human ocular tissues and that the tissues with the highest rate of hydrolysis are similar between humans and pigmented rabbits. A good correlation was also found between the disappearance of the parent compound and formation of latanoprost acid.
Keywords: metabolism • enzymes/enzyme inhibitors