5-methoxycarbonylamino-n-acetyltryptamine and Ocular-Hypertension

We have previously demonstrated that melatonin and its analogue, 5-methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT), reduce intraocular pressure (IOP) in New Zealand rabbits. More recently, we have shown that 5-MCA-NAT can also regulate ciliary adrenoceptor gene expression. Like adrenoceptors, carbonic anhydrase (CA) enzymes are involved in aqueous humour secretion by the ocular ciliary epithelium. Moreover, CA enzymes have been reported to be regulated by melatonin. Hence, the aim of this study was to investigate whether the hypotensive effect of 5-MCA-NAT is also because of a regulation of CA genes and enzymes. Time course of 5-MCA-NAT effect on rabbit IOP was followed for 7 hr every day for up to 144 hr (6 days). 5-MCA-NAT reduced IOP, maximally by 51.30 ± 2.41% (at 3 hr), and the hypotensive effect was maintained for up to 96 hr with a single application. IOP studies with 5-MCA-NAT plus Trusopt(®) and immunohistochemical analysis confirmed that CA are molecular targets of 5-MCA-NAT. In addition, real-time quantitative PCR (qPCR) and immunocytochemical assays were performed to determine changes in CA2 (CAII) and CA12 (CAXII) expression in cultured rabbit nonpigmented ciliary epithelial cells (NPE) treated with 5-MCA-NAT. NPE cells showed a prominent decrease in both CA, at the mRNA and protein levels. These data confirm that the long-term hypotensive effect of 5-MCA-NAT is also due, to a down-regulation of CA2 (CAII) and CA12 (CAXII) expression.

Topics: Animals; Base Sequence; Carbonic Anhydrases; DNA Primers; Immunohistochemistry; Intraocular Pressure; Ocular Hypertension; Rabbits; Reverse Transcriptase Polymerase Chain Reaction; Tryptamines

Melatonin, the MT(2) melatonin receptor agonist IIK7 [N-butanoyl-2-(2-methoxy-6H-isoindolo[2,1-a]indol-11-yl)ethanamine], and the putative MT(3) melatonin receptor agonist 5-MCA-NAT [5-methoxycarbonylamino-N-acetyltryptamine] have previously been shown to reduce intraocular pressure (IOP) in ocular normotensive rabbits. To gain a better understanding of the structure-activity relationship of compounds that activate MT(2) and MT(3) receptors mediating reductions in IOP, novel melatonin analogs with rationally varied substitutions were synthesized and tested for their effects on IOP in ocular normotensive rabbits (n = 160). All synthesized melatonin analogs reduced IOP. The best-effect lowering IOP was obtained with the analogs INS48848 [methyl-1-methylene-2,3,4,9-tetrahydro-1H-carbazol-6-ylcarbamate], INS48862 [methyl-2-bromo-3-(2-ethanamidoethyl)-1H-indol-5-ylcarbamate], and INS48852 [(E)-N-(2-(5-methoxy-1H-indol-3-yl)ethyl)-3-phenylprop-2-enamide]. These compounds produced dose-dependent decreases in IOP that were maximal at 0.1 mM (total dose of 0.259 μg for INS48848, 0.354 μg for INS48862, and 0.320 μg for INS48852) and 1 mM (total dose of 2.59 μg for INS48848, 3.54 μg for INS48862, and 3.20 μg for INS48852), with maximal reductions of 36.0 ± 4.0, 24.0 ± 1.5, and 30.0 ± 1.5% for INS48848, INS48862, and INS48852, respectively. Studies using melatonin receptor antagonists (luzindole, prazosin, and DH97 [N-pentanoyl-2-benzyltryptamine]) indicated that INS48862 and INS48852 activate preferentially a MT(2) melatonin receptor and suggest that INS48848 may act mainly via a MT(3) receptor. The most effective compounds were also well tolerated in a battery of standard ocular surface irritation studies. The implication of these findings to the design of novel drugs to treat ocular hypertension is discussed.

Topics: Animals; Dose-Response Relationship, Drug; Drug Design; Eye; Glaucoma; Intraocular Pressure; Isoindoles; Melatonin; Ocular Hypertension; Rabbits; Receptor, Melatonin, MT2; Receptors, Melatonin; Structure-Activity Relationship; Time Factors; Tryptamines

Melatonin and its analogue, 5-methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT), potently reduce intraocular pressure, and may be good candidates for the treatment of ocular hypertension and glaucoma. After chemical sympathectomy by reserpine or 6-hydroxydopamine, the hypotensive effects of melatonin and 5-MCA-NAT are severely inhibited. This indicates that the sympathetic nervous system is involved in the production and drainage of aqueous humour by the ciliary body and trabecular meshwork, and that it mediates the effects of melatonin and its analogue, 5-MCA-NAT.

Topics: Adrenergic Uptake Inhibitors; Animals; Central Nervous System Depressants; Dose-Response Relationship, Drug; Drug Interactions; Male; Melatonin; Ocular Hypertension; Oxidopamine; Rabbits; Reserpine; Sympathectomy, Chemical; Sympathetic Nervous System; Sympatholytics; Tryptamines; Vesicular Monoamine Transport Proteins