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Abstract #6494 Published in IGR 3-2
Induction of tyrosinase gene transcription in human iris organ cultures exposed to latanoprost
Lindsey JD; Jones HL; Hewitt EG; Angert M; Weinreb RNArchives of Ophthalmology 2001; 119: 853-860
OBJECTIVE: Topical administration of latanoprost sometimes induces gradual iris darkening. The present study was undertaken to determine if latanoprost can increase transcription of the gene for tyrosinase, an important enzyme in the biosynthesis of melanin. Results from brown, hazel, and blue irides were compared. METHODS: Iris tissue was isolated from 30 pairs of post-mortem human donor eyes, and two iris segments from each eye were incubated in tissue culture medium supplemented with 200 nM latanoprost acid or vehicle for seven days. Tyrosinase messenger RNA (mRNA) was determined using real-time polymerase chain reaction analysis (TaqMan quantitative polymerase chain reaction). Results for tyrosinase mRNA were normalized according to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA in each sample. RESULTS: Tyrosinase mRNA expression was similar in blue and hazel irides, and ranged from 0.7- to 12.6-fold greater than GAPDH expression. In contrast, control brown iris culture tyrosinase expression ranged from 6.4- to 265-fold greater than GAPDH expression. Induction of tyrosinase mRNA by latanoprost was below threshold in all the blue iris cultures (n = 8 pairs), present in one of nine hazel iris cultures, and present in five of 13 brown iris cultures. Mean induction in the responding hazel iris cultures was 1.40-fold. Mean induction among the responding brown iris cultures was 2.97-fold. CONCLUSIONS: These observations support the view that iris darkening associated with latanoprost treatment reflects induction of tyrosinase expression. Moreover, they suggest that the probability that latanoprost will increase tyrosinase expression is directly related to the magnitude of tyrosinase expression before treatments are initiated. CLINICAL RELEVANCE: The variability of iris darkening with latanoprost may reflect natural variation in the basal transcription of tyrosinase.
Dr J.D. Lindsey, Glaucoma Center, University of California San Diego, La Jolla, CA, USA
Classification:
11.4 Prostaglandins (Part of: 11 Medical treatment)
