Korean J Ophthalmol.  2007 Mar;21(1):39-44. 10.3341/kjo.2007.21.1.39.

Insulin Enhances Nitric Oxide Production in Trabecular Meshwork Cells via De Novo Pathway for Tetrahydrobiopterin Synthesis

• Kim JW

• KMID: 1105029
• DOI: http://doi.org/10.3341/kjo.2007.21.1.39

Abstract

PURPOSE: To investigate the effect of insulin on the production of nitric oxide (NO) in the trabecular meshwork (TM) cells and the enzymatic synthetic pathway of tetrahydrobiopterin (BH4) synthesis. METHODS: Primarily cultured human TM cells were exposed to 1, 10, and 100 microgram/ml of insulin and 0, 1, 10, 100 and 1000 nM dexamethasone for 3 days. To evaluate the enzymatic pathway of BH4 synthesis, 10 micrometer dexamethasone, 5 mM diaminopyrimidinone, 100 micrometer ascorbic acid, 100 micrometer sepiapterin, or 10 micrometer methotrexate were also co-administered respectively. Cellular survival and NO production were measured with MTT and Griess assay. RESULTS: Insulin enhanced NO production in a dose-dependent manner significantly (p<0.05) without affecting cell viability, whereas dexamethasone inhibited NO production. With co-exposure of insulin, diaminopyrimidinone and sepiapterin inhibited insulin-induced NO production. Ascorbic acid increased NO production independent of insulin and methotrexate did not affect to the action of insulin in NO production. CONCLUSIONS: Insulin increases NO production in TM cells via de novo synthetic pathway for BH4 synthesis. Insulin could be involved in the regulation of trabecular outflow by enhancing NO production in TM cells.

Keyword

Dexamethasone; Insulin; Nitric oxide; Tetrahydrobiopterin; Trabecular meshwork cell

MeSH Terms

Trabecular Meshwork/cytology/*drug effects/*metabolism/physiology
Nitric Oxide/*biosynthesis
Insulin/administration & dosage/*pharmacology
Humans
Dose-Response Relationship, Drug
Cells, Cultured
Cell Survival/drug effects
Biopterin/*analogs & derivatives/biosynthesis

Figure

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  Fig. 1 Effect of dexamethasone on the production of nitric oxide in cultured trabecular meshwork cell exposed for 3 days. Dexamethasone decreased nitric oxide production. (*; p<0.05)

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  Fig. 2 Effect of insulin on the production of nitric oxide on cultured human trabecular meshwork cells. Insulin increased nitric oxide production in a dose-dependent manner and inhibited by 0.5 mM L-NAME (Nω-Nitro-L-arginine methyl ester). (*; p<0.05)

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  Fig. 3 Effect of 10 µM dexamethasone on the production of nitric oxide after co-exposure to insulin. Dexamethasone did not affect insulin-induced production of nitric oxide significantly. (*; p<0.05)

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  Fig. 4 Effect of 5 mM diaminopyrimidinone on the production of nitric oxide after co-exposure to insulin. Diaminopyrimidionone abolished insulin-induced production of nitric oxide. (p>0.05 at each group)

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  Fig. 5 Effect of 100 µM sepiapterin on the production of nitric oxide after co-exposure to insulin. Sepiapterin abolished insulin-induced production of nitric oxide. (p>0.05 at each group)

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  Fig. 6 Effect of 100 µM Lascorbic on the production of nitric oxide after co-exposure to insulin. L-ascorbic acid increased nitric oxide production and abolished insulin-induced production of nitric oxide. (p>0.05 at each group)

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  Fig. 7 Effect of 100 µM methotrexate on the production of nitric oxide after co-exposure to insulin. Methotrexate did not affect insulin-induced production of nitric oxide significantly. (*; p<0.05)

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