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The melatonin analog 5‐MCA‐NAT increases endogenous dopamine levels by binding NRH:quinone reductase enzyme in the developing chick retina
Author(s) -
Sampaio Lucia de Fatima Sobral,
Mesquita Felipe Pantoja,
Sousa Paulo Robson Monteiro,
Silva Jerônimo Lameira,
Alves Claudio Nahum
Publication year - 2014
Publication title -
international journal of developmental neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.761
H-Index - 88
eISSN - 1873-474X
pISSN - 0736-5748
DOI - 10.1016/j.ijdevneu.2014.09.001
Subject(s) - dopamine , endogeny , chemistry , antagonist , biology , receptor , medicine , biochemistry , endocrinology
NRH:quinone reductase (QR2) is present in the retinas of embryonic and post‐hatched (PH) chicks. 5‐Methoxycarbonylamino‐N‐acetyltryptamine (5‐MCA‐NAT) is a QR2 ligand that increases cAMP levels in developing retinas, but it does not affect cAMP levels in CHO‐QR2 cells. The dopamine quinone reductase activity of QR2 retrieves dopamine, which increases cAMP levels in developing retinas. The objective of the present study was to investigate whether 5‐MCA‐NAT increases endogenous dopamine levels in retinas from chick embryos and post‐hatched chicks. Endogenous dopamine was measured by enzyme‐linked immunosorbent assay (ELISA). 5‐MCA‐NAT increased retinal endogenous dopamine levels at all developmental stages studied and in PH chicks (−log EC50 = 11.62 ± 0.34 M). This effect was inhibited by non‐selective antagonists of receptors and melatonin binding sites N‐acetyl‐2‐benzyltryptamine (luzindole, 5 μM), but it was not inhibited by the Mel1b melatonin receptor antagonist 4‐phenyl‐2‐propionamidotetralin (4‐P‐PDOT, 10 nM). The QR2 cosubstrate, N‐methyl‐dihydronicotinamide (NMH) (−log EC50 = 6.74 ± 0.26 M), increased endogenous dopamine levels in controls and in retinas stimulated with 5‐MCA‐NAT (3 nM). The QR2 inhibitor benzo[e]pyrene inhibited endogenous dopamine levels in both control (−log IC50 = 7.4 ± 0.28 M) and NMH‐stimulated (at 100 nM and 1 μM benzo[e]pyrene concentrations) retinas. Theoretical studies using Molegro Virtual Docking software corroborated these experimental results. We conclude that 5‐MCA‐NAT increases the level of endogenous dopamine via QR2. We suggest that this enzyme triggers double reduction of the dopamine quinone, recovering dopamine in retinal development.